Everyone knows as long as you fall the right way, a volcano can never hurt you.
Look. Oda nuked Pell and gave him a death and mourning scene and he was fine.
Pound just did not die somehow.
Saul is alive after being frozen and exploded by an armada of canons
So for characters that were in universe stated to be monsters - Big Mom had to get Oda to invent rules about Laws Awakening only to break them 5 seconds later and Kaido was fighting evenly with One Piece Jesus - I just don’t buy a volcano is enough. Especially when Luffy does not kill.
If people die we get told in no uncertain terms. And even then bringing back Acd was not out of possibility.
Although to be fair it was Wano and Oda had to confirm Orochi was dead in an SBS, so who knows?
Kaido’s dream was to fight and die to Joy Boy and it was clear he did everything to that end and Luffy really did not seem to hate him. So he might of got his wish. But again, i feel Oda would confirm that.
I think he’s going to be back honestly to whip Momo into shape.
People in universe don’t seem sure and Nami has Big Mom’s card. There’s an easy way to confirm this and he hasn’t taken it. Meaning he’s either forgot and no one has asked yet or he has plans.
And his remarks regarding the Dragon Fruit seem to suggest he has plans…
Honestly had Canon is Kaido is just chilling in a Lava Bath content with life