As Fish said, the science isn’t yet detailed enough to know for sure the true answer. But so far a few things are reasonably certain …
A mind is NOT simply software running on fixed hardware, where you can take a copy of the software and capture 100% of the dynamics for potential later reload into any other standardized human brain.
Your brain and mine are wired very differently. They grew inside different heads, exposed to different environments, both sensory and internal bichemical, and they derive from different genetic programs. They’re grossly similar, but vastly different in detail.
So your “tape” won’t play on my “player” and vice versa.
It’d be sorta like trying to take a block-by-block copy of a drive through New York City and replaying the turns & distances back on a car in LA. Pretty soon you’d drive through a building and the program would crash. You’d definitely not end up at the same desitination even if you perfectly duplicated the turns & straightaways.
So that pretty well kills the idea that person A’s backup tape could be inserted into Person B’s body, thereby effectively reincarnating A’s personality and making personality B disappear.
But it’s worse. Your own brain changes continuously. Yes, it’s pretty slow once you’re an adult, but it does change. So we might be able to make a backup tape of you on Monday and reinstall that tape into your brain on Friday. You’ll lose the interveneing week, but otherwise it’d work pretty good.
That might be useful if something really awful happend that week that you’d rather not have experienced. (witnessed ghastly crime, etc.)
But if we tried to install the same tape in you 6 months later it might not install real well. Your brain will have changed enough that the tape no longer runs right. You might have major memory loss, or personality problems or, well, who knows.
It’d be the human version of Windows “DLL hell”, where installing different programs overwrites chunks of Windows’ code with varying and incompatible versions of the same code files.
To accurately capture a backup, you’d literally need a star-trek transporter gizmo that captured the complete arrangement of the hardware & software: the cells and their connections and internal chemical states as well as the current pattern of electrical stimulation.
That’s a tall order.
[I’m not a brain researcher, but that’s an area I’ve followed as an interested layman since college, lo those many years ago.]