This belief is really starting to bug me because it just show that people don't care about the narration of One Piece.
Narratively, why do you think Kaido and Big Mom were both put in a magmatic chamber before a gigantic explosion?
Well let me tell you:
It's because Kaido and Big Mom are BOTH considered equal to natural calamities, one being a hurricane, the other being thunder.
What Oda did here, is a return to the natural order. In other word, Luffy, Law and Kid punished Kaido and Big Mom and send them back to the "natural" hell they came from.
This panel:
Is a destruction panel, a desintegration of the physical form, to create this:
Thus, Luffy returned Kaido to nature and nature answer by taking Kaido back and declaring Luffy the victor. This, is the narration of the
DEATH of Kaido and Big Mom, symbolic AND physical.
So when you or the fanbase try to explain us that "somehow, they lived"... you literally scrap the beauty and writing of this moment away. You render these few pages meaningless.
This moment is a Dragon Ball like desintegration, it is meant to represent the end of both of these character, an end that can only come from the most powerfull force on the planet.
There is absolutely no reason to bring Kaido or Big Mom back to life or have them interact. It would be really damaging to the story to actually bring them back physically.
Now this doesn't mean they won't. As I theorized, we might go to hell, we might literally stumb upon these falks once more. But it won't be the same type of character.