So what's the answer? The answer was to never touch Master Chief or that timeline again, let him forever float towards that mysterious planet. Instead focus on side stories, smaller skirmishes and scale, different timelines, alternate perspectives of the original trilogy, etc.
The only real paths Halo could have gone down would have been making a new trilogy where you fight the insurrectionists OR just making random spin offs set in the Human-Covenant War, I personally cannot think of a way to have a new trilogy that would be as epic as Bungie's.
It depends. Star Wars managed to make a great Expanded Universe series with the continuing adventures of Luke and friends, like the Thrawn Trilogy, Crimson Empire, Dark Empire, and the Jedi Knight games, but those were written by writers who weren't concussed orangutans. Halo went off the deep end after 4 and never came back. Halo 5 onwards, the story-writers were just throwing shit on the board.
It's no secret that the best media of Star Wars outside of the OT are ones that don't try to follow mainline lore, like KOTOR for example.
Hell, it'd be funny to see things like the earlier years of the Human-Covenant War, as well as the Grunt Rebellion and the Taming of the Hunters.
With the former, we can play as Spartans or marines who have weaker armor as players, a la Halo Reach or ODST. In the latter, we can play as the Arbiters as they keep the Covenant together during trying times.
Speaking of the Covenant, it would be fun to have a Dynasty Warriors: Empires sort of game where you play as a Covenant Warlord and fight to control it all after the Covenant splintered into warring states.
It also didn't help that 343 wrote themselves into a corner. They wanted to kill off Cortana to pull the emotional strings, but in doing so erased a large part of what made Halo "Halo." So they bring her back, but this time as a villain as a comprise, and in doing so further desecrated her character. And for what? A terrible story that went nowhere. Now we have fake Cortana in Halo Infinite as a band aid fix. You could have just done nothing at all and be in the same position.
Halo 5 should've been a struggle by the Chief to revive Cortana, with him having a Cortana fragment and going from one Forerunner ruin to another to find a way to bring her back. Then have it so that Team Osiris was dispatched to hunt him down because he went AWOL from his post trying to revive Cortana.
When John finally succeeds, with some help from Forerunner constructs like the Warden Eternal, Team Osiris catches up to him and guns him down, leaving him critically injured. The sight of UNSC Spartans nearly killing the Chief then causes the newly-revived Cortana to go rogue.
Halo 6 won't feature the Chief, but have ONI be the bad guys, and Cortana hires a certain Brute and his PMC to help with kicking the shit out of ONI and their pawns within the UNSC-the Banished. Atriox becomes a playable character, with Cortana's guidance, and you have to help free the UNSC from ONI's control. First mission: save Dr. Halsey before ONI assassins dispose of her for no longer being useful.
There you go. Once again, I came up with a better story than people who are paid professionally to make up stories. In less than five minutes.