If someone gets cremated or buried long enough for eir brain to fully decompose into dirt, it becomes extremely difficult to revive em. Nothing short of a vastly superhuman intelligence would have a chance of doing it. I suspect that it would be possible for a superintelligence to do it, but unless there's a more efficient way to do it, it would require recomputing the Earth's history from the time the AGI is activated back to the death of the last person it intends to save. Not only does this require immense computational resources that could be used to the benefit of people who are still alive, it also requires simulating people experiencing pain (backwards). On the other hand, this saves people's lives. Does anyone have any compelling arguments on why an FAI would or would not recreate me if I die, decompose, and then the singularity occurs a long time after my death?
Why do I want to know? Well, aside from the question being interesting in its own right, it is an important factor in deciding whether or not cryonics is worth-while.