There’s another potential wrinkle in here: what if someone is convicted for murder and then the victim comes back to life?
Actually, this one is could be pretty straightforward: if the victim was actually dead at some point, i.e. he really was dead, he wasn’t simply missing or presumed dead, then the elements of the crime are still complete. The defendant did, in fact, kill the victim. Whether or not the victim stays dead is not actually an element of any homicide offense. So it would seem that this is ultimately irrelevant, which is perhaps a little counter-intuitive but does have the benefit of simplifying things a lot. As courts tend to like rulings which alleviate the burden on their dockets, this is not an unlikely outcome.