Derek Parfit (a philosopher), in "Reasons and Persons", considers many of the cases you hint at, as well as few more tricky ones (such as progressively replacin

Derek Parfit (a philosopher), in "Reasons and Persons", considers many of the cases you hint at, as well as few more tricky ones (such as progressively replacing your brain cells with someone else's, or splitting someone's brain [1] and putting the two halves in different bodies). He ultimately argues for two points: 1. Personal identity is basically just psychological continuity (physical continuity doesn't matter). That psychological continuity needs to be "non-branching" -- identity has to be one-to-one, and so if there's a clone of you walking around, it makes more sense to say neither of you are "you" than to say "both" are. 2. As the weirdness in (1), suggests, Parfit doesn't think personal identity matters very much. Self-interest (as opposed to altruism) seems a little silly when you linger on who exactly you care about, especially in the face of blended-brains and split-brains. If we were immortal but had finite memory, Parfit would argue that personal identity is more of a sliding window. As we forgot our ancient memories, we would lose touch with that part of ourselves, eventually becoming totally distinct persons over time. Which, of course, sounds a lot like the actual human condition. [1]: https://en.wikipedia.org/wiki/Split-brain https://en.wikipedia.org/wiki/Split-brain