Time travel / alternate reality bring back dead people
I feel like Back from the Dead can be split into subtropes Inversion of Ret Gone and often a side effect of it. Long dead characters come back from the dead after someone go back in time and prevent them from dying. Or they turn out to be alive in alternate universe, where their killer fails, refuses or doesn't exist at all. Godwin's Law of Time Travel is when entire Third Reich experience that. Compare Reset Button when recent death is canceled in the end of the same story.