Brain gets no more blood. Neural biochemistry breaks down. Brain dies. You die. That’s it. Except for some incoherent and contradictory texts from bronze-age books or wishful thinking by naive people, there is ZERO scientific evidence that heaven or reincarnation exist. Even Buddha never suggested we would reincarnate, that was an idea added later by some of his followers. The bible is very flimsy on the entire concept of hell and heaven.

If quantum immortality is real, things might get really weird the closer to the end you get. The idea is if there is an infinite multiverse and our consciousness experiences one of them, then it could pick the “best” one, by some definition of “best”. In which case unlikely things that can keep your life going (and be worth keeping going) are more and more likely to happen as you exhaust the more likely possibilities that would end your life. Could be that each of us ends up immortal in our own universe, not really alone because other people are there but alone in that their consciousnesses aren’t likely present (unless your best unlikely future is also theirs).