World's Likely a Simulation, So Look for Snapshots Subsystem
If the universe is like a computer, and we live in simulated reality, then one possibility is, that just like we sometimes save the state of a computer program to a cold storage, and then can recover it any time, the universe may also have a backup mechanism, that stores its states.
A scientific research could in principle be carried out to try to discover such mechanism if it at all exists. Then, in order to take the dead from the past, we would have to simply take isolated objects from one state, and re-instantiate them in another state (i.e., just like transferring a variable from one virtual machine to another.)
For the beings incorporated this way into the future, it would be possible to visit, for example, their own grave. We could also begin working with this kind of variable transfer from saved states, to see, how this overall works, and what phenomena we should look for in our world to discover the world's snapshots mechanism if such exists.