If you isolate a single Everett branch and look only at that branch and not all the other branches, and run that branch backward in time, it will evolve into a multiplicity of pasts (that would in the greater scheme be coherently canceled out by the past evolution of other branches). The upshot is that even if you timeslice the entire future lightcone in a single branch you cannot get the exact past. And we can't get photons that have escaped over the horizon, so we can't get the whole future lightcone anyway, and small divergences will amplify, and the whole thing would require more computing power than all the particles we're trying to run back.

Then use the quantum 'probability' distribution over pasts to randomly pick a person to instantiate (more properly, pick a past and instantiate everyone in it). If you got the distribution right, then each resurrectee has the same relative measure they did before they died (original measure times fraction of worlds in which you do this). Obviously, you can also do this with subjective probability distributions derived from locally available information.

Just how much good this does for the dead is hard to say.