What is the probability of having afterlife in a non-magical universe?

Aside from the simulation hypothesis (which is essentially another form of a magical universe), there is at leas one possibility for afterlife to exist: human ancestors travel back in time (or discover a way to get information from the past without passing anything back) to mind-upload everyone right before they die. There would be astrong incentive for them to not manifest themselves, as well as tolerate all the preventable suffering around the world: if changing the past leads to killing everyone in the original timeline, the price for altering the past is astronomical. Thus, they would have to only observe (with the reading of brain states as a form of observation) the past, but not change it, which is consistent with the observation of no signs of either time travelers or afterlife. But if will happen in future, it means it's already happening right now. How do you even approach estimating the probability of that?