An upload will become a file, a string of bits. Said file could then be copied, or even irreversibly mixed if you prefer, into many such files, which all share the same causal antecedents. But we could also create an identical file through a purely random process, and the randomly-created file and the upload file are logically/physically/functionally identical. We could even mix and scramble them if desired, but it wouldn't really matter because these are just bits, and bits have no intrinsic history tags. You have spent some time dismantling zombie arguments, and it would seem there is an analog here: if there is no objective way, in practice/principle, to differentiate two minds (mindfiles), then they are the same in practice/principle.

On the other hand, I doubt that creating a human-complexity mindfile through a random process will be computationally tractable anytime soon, and so I agree that recreating the causal history is the likely path.

But if you or I die and then one or the other goes on to create a FAI which reproduces the causal history of earth, it will not restore our patterns through mere coincidence alone.

Curious though, as I wouldn't have predicted that this would be your disagreement. Have you written something on your thoughts on this view of identity?