With a little bit of research, including the books that Miura heavily drew inspiration from, clues from the original chapters, foreshadowed moments and key plot points, I'll try to see if Miura ever hinted at how Berserk would end.
Spoilers below
For the time being, lets bring up major plot points repeatedly brought up in the past:
- Guts has a soft spot for children, but his son and griffith share the same body.
- Guts is also extremely proud of his own humanity and vulnerablity
- Godhand are replaced cyclically. Therefore, they can be killed.
- There is a behelit. It has not been used at all during the events of the story. This means that this behelit will have something to do with the final confrontation, and its activation is critical to resolving the end of the story. It is also only activated for a specific emotion or desire. The will to live is different from the fulfillment of a dream, and you can only achieve this by sacrificing something of actual value.
- The behelit can be fit into guts’s cannon.
- Sacrifices do not have to be completed for the power to transfer. The sacrifices have to merely be branded.
- Gaiseric’s kingdom being sacrificed is a foreboding of future events, the mirroring of causality's spiral.
- The astral world and the physical world have merged, and thus the godhand can now assume physical bodies that can be destroyed, since the astral dimension can no longer be separate from the physical one.
- Humans who used behelits return to their original state after their power is taken away from them. Also, when the astral plane is opened, the souls of hell will drag all those who were involved with demons, regardless if they were apostles or not.
- The “one on ones” between griffith and guts on the hill of swords have been cyclical. 1st time, griffith won, 2nd time guts won, 3rd time griffith “won”. This is because causality acts in spirals, not in linearity, and events tend to mimic history and repeat it. Thus, there was an eventual fourth confrontation that had to conclude, which guts would win. Thus, Miura has always planned for Guts to win in the end.
- Guts is shown to be creative and quick on his feet, meaning that he comes up with solutions that no one dares. This is critically important.
- Evil is its own undoing. That is critical to the story.
- The massive hole at the tower of rebirth could point to there being the root of a tree there, and the mages could have split that tree from the physical world in a last ditch attempt to thwart a former godhand's plans. The entire kingdom sinking on its own is unlikely.
- Casca possesses strong motherly instincts for the moonlight boy. This conflict between guts and casca is foreshadowed.
- The best way to kill something as enormous as the sea god and its minions is a stab to the heart. This is probably foreshadowing for later, as in the only way to take away the powers of the godhand and the apostles is also a stab to the heart.
- The count refuses the godhand in the first few chapters, this implies that causality is not absolute and the godhand cannot predict the future, as well as the fact that humans can choose their outcome even if they are presented limited options
- The beast of darkness would return. This was foreshadowed multiple times. Knowing Miura, the beast of darkness would most likely have come at the inflexion point most critical to the story.
- The moonlight boy can supress the effects of the brand. This is why guts and casca don't die immediately even though Griffith and the moonlight boy are the same person.
- Miura is an excellent writer that puts a lot of thought into the details of his story, so we can actually have clues to the end of the story by analysing the meaning of “Guts” and “berserk”.
- One of Guts’s strongest qualities is how brave he is. He endlessly fights fate, never giving up hope, and in a world like Berserk’s which is 1000 times worse compared to our own, it just goes to show how much courage he possesses, or how much guts he’s got. But that courage could also point out to his resolution as a character, i.e guts chooses to let the past go, and move on. In other words, Guts will not kill Griffith, because letting the past and hatred go is one of the bravest things a person can do. (This will come to a conclusion we call point X, which is where everything ties together in one final battle)
- The IoE proposes that the strength of the Godhand and the strength of the apostles comes from the collective unconscious belief of humanity (a very Jungian way of thinking). Thus, we can also conclude that in some manner, the loss of faith in griffith’s kingdom in some manner will also severely weaken the faith the people of his kingdom have in him. The fall of Griffith’s republic will also be critical to the parallels between guts and griffith: Griffith destroyed everything guts held dear to him in front of his very eyes. Therefore, somehow Griffiths republic will break down in front of his very eyes (The foreshadowing being the count in the inital few chapters of the story, where the daughter see the count for who he really is, in the same way the republic will see griffith for who he really is. Causality mirrors the past).
- The idea of evil is a defenseless heart, and betrayal feels like a stab to the heart. Therefore, Guts's revenge against Griffith's stab to his heart would a metaphorical stab to Griffith's heart, aka the Idea of Evil, which gives the Godhand and the Apostles their power.
- The defeat of Griffith involves destroying his dream to own a kingdom right before his very eyes. Just like what Griffith did to Guts so many years ago, everything would have come back to him. Griffith doesn’t care about the actual kingdom itself, but instead he cares about owning possessions. So the rebelling of Falconia will involve the citizens outright disobeying him.
- The moonlight boy is extremely powerful, and can control other astral creatures, use strong magic and can even overpower Griffith for control on a full moon. This ridiculous level of power that can surpass a godhand might be important for later.
- The world tree is helical, so is the root of the Idea of Evil in chapter 88.
- The branded can make sacrifices, but cannot be rebranded. Guts could not be sacrificed because he was already marked, but the Egg apostle was branded and was an apostle simultaneously.
- For some reason, I believe that the world tree’s destruction will be in conjunction with the fall of griffith’s kingdom. This is probably because the world tree is a reference to the ancient Norse Yggdrasil, since Miura loves mythology. The severing of the world tree will be critical, since all the other trees have been severed to allow the world tree to accumulate power. Berserk is trying to draw influence from various mythos, like Ragnarok, Armageddon and Kaliyuga.
- Now we get to the title, ‘Berserk’. To go “berserk” means to go out of control with rage and hate, and good authors always use their titles as a clue to the ending of their story. So my best guess is that at the end of the story, all three main characters will go berserk. Casca goes berserk over her son, Guts goes berserk over something happening to casca as well as seeing griffith, griffith goes berserk over guts destroying his dream and taking away his control.
Based on the all the facts above and hrough some guesswork, we can see that Falconia is actually the antithesis to Griffiths powers. The Idea Of Evil thrives on endless suffering to maintain its existence, and the building of a utopia would negate that since all suffering would be removed. However, the Idea of Evil is not comfortable with its existence trapped in the astral world, as it merely exists for the sake of existing without any control (Godhand members are only powerful during interstices and can otherwise do absolutely nothing except influence thoughts, and people who become godhand members do after being put into a state of existing for the sake of exisiting. Godhand members only derive power to manifest through collective belief). By sacrificing all of humanity, the Idea of Evil can trade places and will no longer be dependent on human whim to exist.
Some guesses:
- Causality doesn't exist, the Idea of Evil is a liar just like its servants and exists to merely deceive. What the Idea of Evil can do is insert specific thoughts and ideas into human beings, and said human beings only know how to believe it and think it came from them, when truth is it came from the idea of evil. The idea of Evil is defenseless and has no agency, but through the godhand who have some degree of agency can bring about its ultimate goal. The godhand are also basically very good salesmen, by bringing about certain conditions that force you to pick the cards that they play, while also playing specific roles in the story. The key point here is that the Idea of Evil can predict the consequences of thoughts they introduce, but not the consequences of the actions resulting, as well as the choices that people make against their innermost desires. This is why the godhand can predict the eclipse and SkullKnight attacking Griffith, but remain dumb about moonlight boy and Guts. The more the people they influence, the higher the chances of their actions coming to fruition. They have a high chance of causality's accuracy, but a very small margin of error. SkullKnight fights against the godhand by accumulating the margins of error through compound interest/butterfly effect, eventually having those small errors build up into large game changing consequences, essentially playing the Godhand's game against them.
Based on this guesswork, I assume this is how it would have followed.
A conflict befalls elfheim, and guts, after unlocking th full potential of the berserker armour, probably kills a major apostle in the battle, most likely grunbeld. The gang somehow makes it to Falconia, guts gets a new sword and weapons from Rickert and in some way they get Falconia to see the true nature of griffith (this most likely has a lot to do with Sonia's ability to communicate telepathically, and schierke's mind transfer. The timing should be around Griffith's coronation ceremony). Thus the entire kingdom rebels against Griffith. This puts a cog in griffiths plans, meaning they have to sacrifice falconia quickly, in order to physically bring the IoE into the real world at the base of the World Spiral Tree. As the sacrifice process takes place (remember they just have to be branded, they do not have to die yet), the Idea of Evil materializes at the bottom of the world spiral tree and “connects” to it. Guts and gang fight an initially depowered horde of monsters because of the loss of faith of the entirety of humanity in griffith(probably after guts unlocked the full power of the berserker armor allowing him to take on Zodd and Grunbeld, or some other plot point miura planned for). At some point in the conflict with everything falling apart, a full moon befalls the kingdom on a cloudy night. Point X happens (I have no idea how he planned to write it)
- Guts, casca and griffith meet, and three battles happen at once: Guts vs Griffith, Guts vs the Beast of Darkness and Griffith vs the inner moonlight boy. Guts gets the upper hand because Griffith cannot use his full powers and is overpowered by guts. But as his hair slowly turns more and more black, Casca realizes that Griffith is the moonlight boy, her son. This makes Casca get in the way of Guts delivering the final blow.
- Griffith comes back momentarily (because of some unknown factors), uses a burst of energy to render guts broken and defeated, and in his desperate attempt for regained control decides to, in great difficulty, attempt to rape Casca a second time right in front of a completely broken guts(or something else that makes guts sink to his lowest point). Guts being helpless after the berserker draws out too much blood, goes berserk, and the behelit activates.
- The behelit activates, guts/casca is given the choice to accept or reject the behelit by sacrificing casca/guts. I believe this is going to be Guts because he is always proud of his humanity. Alternatively, both of them are presented with the choice of sacrificing each other. (I believe this to be the case even though casca and guts are branded because this ties into the beast of darkness's hatred for casca, since casca prevents the realization of its goals. So somwhere along the plot, there's going to be a situation where guts will struggle against the beast of darkness who wants to sacrifice casca for the realization of its goals.) Why would this happen? Well firstly, maybe gut's party is too close to destroying the godhand and the idea of evil would rather kill a single godhand member over having its plans ruin. This is because there is no trust in a den of thieves. The point is that Guts will be made an offer he can't refuse, but ultimately will refuse, why this exactly would happen I have no idea. I think Miura wants to show us the difference between guts and Griffith when all hope is lost. Will guts sacrifice the band of the hawk and everything he holds dear just to realize his burning desire? And I think the answer is no, Guts will not sacrifice his friends like Griffith did, even if it will cause him to lose everything.
- I think its most likely going to be Guts because that will tie in to the theme of guts being proud of his humanity. Guts will reject the Behelit after choosing to let go of his hatred of griffith and his ptsd, but will be dragged into the Abyss with his armour. Fortunately, Schierke will know that the abyss now no longer exists in a separate reality, but at the bottom of the world tree. Soon , the full moon completely befalls Falconia, and griffith is replaced by the moonlight boy. Casca asks the moonlight boy to go save his father, calling him by his name and the moonlight boy rushes after guts in the abyss.
- Guts is dragged down into the depths of the abyss, fighting the evil souls as he goes all the way down. With him, he carries a very large sword. I think its possible that the moonlight boy also comes to him to ward off the souls, considering that the moonlight boy is almost as powerful as femto himself. This is already kind of hinted at, the Path of Dragons being severed by the Dragonslayer. Point being, guts will travel to the bottom of the abyss.
- Using the now massively overpowered sword of actuation/dragonslayer hybrid (or maybe just a bigger dragonslayer) Guts, embodying pure human willpower, will stab the Idea of Evil, effectively nerfing the godhand and taking their power away, just like how stabbing the Sea God's heart took the power of the sea monsters away.
- The world spiral tree is somehow severed (the exact method was probably going to be outlined in the fall of Elfheim with the witches) just seconds before schierke and farnese can pull guts and the moonlight boy out. What happens is that the astral world and the physical world are now going to be permanently disjoint, since the world tree is the last one bridge between both worlds. This keeps the physical world away from the undead spirits and other evil creatures, ushering a new milennium of peace and tranquility.
- The godhand’s bodies are now reduced to their original forms, and they are consumed by the vortex of souls, for that is the fate of those that deal with demonkind. I do not know how the next bit will happen, but after rereading berserk my belief is that Griffith will be taken to hell by the souls of the original band of the hawk in his weakened body (just like how the count was taken to hell by the doctor) while the moonlight boy’s body is somehow severed from him since it doesn’t belong to griffith and is a physical one (since godhands exist only in astral planes while apostles exist in physical planes, and the slow severance of the world tree will effectively “peel” griffith off of the moonlight boy just like how Schierke peeled the BOD off of guts, since Griffith already sacrificedhis corporeal form to the IOE). Griffith only possesses the astral body, and as such when the moonlight boy and guts ascend out of the world spiral tree he is consumed by the vortex of souls, this happens during the process of it slowly being severed. Before griffith falls to the vortex of souls, we see his tortured face for one final time.
- Guts exits from the world tree with help from Schierke’s astral projection and the moonlight boy, and the world tree is severed, dooming the godhand to never ending hell and having them being completely cut off from the physical world forever. The killing of the Idea of Evil as well as the sealing of the astral world completely will have Guts and Casca ultimately be free of their fate to die, and thus they overcome their supposed “destiny".
- Guts, Casca and the Moonlight boy live happily ever after, as a family, in a world free from monsters, demons, war and fate. Having used the berserker armour to its full potential renders Gut's hair completely white, and he lives the rest of his life as a disabled veteran, taken care of by his friends and family.
Edit:
After going through some more links, I believe that additionally, Casca will lead huge war against Falconia, basically Band of the Hawk vs Band of the Falcon. Zod will betray also betray Griffith.