I've kind of switched to the view that I'm an observer-moment (OM) rather than an observer. There could be a giant probability distribution over all OMs that's based on complexity or something else, I don't claim to understand it.
Since some OMs remember being other OMs, we imagine a single thread of continuity pointing backward. (If minds could merge, we'd get creatures that remember being both Alice and Bob, so their past would look more like a tree, but we don't have the right technology yet.) Since we are also inductive learners, we imagine that continuity points forward as well. Since that seems to contradict physics, we compromise and say "okay, I have multiple actual futures, but there's gotta be a probability distribution over the next OM".
But I don't see why such a distribution must exist! At most, you have a distribution over OMs that have an (imperfect, possibly false) memory of being your current OM. You could call it immortality, but I'm not sure that's the right way to think.
Wow, that was a mouthful. Hope that makes sense to anyone else...
The continuing identity of a person seems to me the same sort of thing as the continuing identity of a physical object, and not particularly problematic. The paradox of Theseus' ship is as easily dissolved as that of unheard falling trees.
I have a day-to-day continuity that I do not have with any part of anyone else since I was born, in just the same way that the chair I am sitting on does not have any continuity with any other chair more recently than when it was assembled on a production line.
To ask whether a person who has undergone a massive change of ...