Tips: figure out if MWI is correct before you start worrying about these things. The existential crisis that can be brought on by thoughts surrounding QTI and QTorment can induce suicide and other bizarre behaviour. This is the reason that Jacques Mallah wrote a paper on the fallacy of quantum immortality, because he estimates the risk is too high that people will start dying over this interpretation.
Now as Mitchell Porter says, MWI got some problems, mainly the Born Rule and Preferred Basis, aswell as problems with having wavefunction realism in configuration space/relativity (prompting proponents of MWI such as Wallace to postulate Space-Time state realism) this is enough for the vast majority of physicists to reject MWI, even some of the early supporters like Weinberg has turned his back on the hypothesis.
But even if you do believe Many Worlds is true, you have to factor in another thing: we don't know whether worlds branch or diverge. Alastair Wilson and Simon Saunders have written about this, the math doesn't decide, so we can't know. It could be that once two outcomes can occur you "branch" into both worlds, or it could be that we are already on 2 separate, but identical worlds and when two outcomes occur, only one occur in the branch you are already isolated on. If this is the case, then quantum immortality is falsified 100% bcause you will forever remain on a single branch until the end of time... This also solves the "incoherence" problem with probability and lets us keep our episteomology.
Last, but not least I want to raise some criticism of Yudkowsky and Tegmark for introducing such ideas as fact, when there are severe problems facing it. It may have caused a lot of suicides from mentally unstable people, existential crisis and people who just thought quantum roulette would be a good way to get a better life, people who don't care about the overall measure. All because of something that is highly speculative with seemingly insoluble problems.
this is enough for the vast majority of physicists to reject MWI
Cite, please.
we don't know whether worlds branch or diverge
It's a field. There's no meaningful distinction here.
If the many worlds of the Many Worlds Interpretation of quantum mechanics are real, there's at least a good chance that Quantum Immortality is real as well: All conscious beings should expect to experience the next moment in at least one Everett branch even if they stop existing in all other branches, and the moment after that in at least one other branch, and so on forever.
However, the transition from life to death isn't usually a binary change. For most people it happens slowly as your brain and the rest of your body deteriorates, often painfully.
Doesn't it follow that each of us should expect to keep living in this state of constant degradation and suffering for a very, very long time, perhaps forever?
I don't know much about quantum mechanics, so I don't have anything to contribute to this discussion. I'm just terrified, and I'd like, not to be reassured by well-meaning lies, but to know the truth. How likely is it that Quantum Torment is real?