Presumably if the matter warping is sufficient to kill him then he just comes back to life again. Same as when he gets crushed flat or blown up he still seems to come back.
Reality warping... well, in it's crudest form of say blowing him to pieces or scattering his atoms, maybe it all counts as death once he is beyond the point of functioning and he just comes back. But if someone just turns him into glass, or rewrites his DNA so that he is no longer Homo Supreme, or destroys his actual soul... not so sure that he is just coming back from that.
Another limit would be just encasing him in adamantium and throwing him into the deepest ocean. Might get out eventually like when the universe is dying but he would probably be completely insane.
Originally posted by Sin I AM
For all intensive purposes i believe he is the one true immortal in dc. At any point his heart stops he just automatically comes back. I dont think that rewriting his dna or anything of that matter would work. He seems to be above that
Educated guess.
How Mr. I comes back to life is unclear, as its he's never shown regenerating ala Wolverine. What he has is not some insane HF; he's Supreme, not Superior.
He's going to outlive this universe.
So, i'd say he comes back from what you asked/suggested.
You can read all that and say nah, you're assuming, but i actually put some thought into my answer.