I'm trying to avoid assuming a metaphysic where simulations are assumed to be possible, because I'm not sure such metaphysics ultimately make sense. (Maybe you can guess my rationale: I think "measure" and "existence" and so on are very fuzzy, and I think if we reason in terms of decision theoretic significant-ness then it might turn that running a simulation of something doesn't double its "measure", and what matters is what already "actually existed/exists", i.e. what's already "actually significant".) If you don't assume a simulationist metaphysic then "rescue sims" are dubious, whereas reviving people who are known to have already existed seems more like a straightforward application of technology. If you take a sort of common-sense layman's perspective, reviving the dead sounds a lot less speculative than running an exact simulation of a mind on a computer in a way that will actually change the past. ...No?
The layman's perspective sounds reasonable enough, but seems to fall apart on closer inspection. What makes a human brain different from a simulation? Why would the AI have an easier time reconstructing the mind of someone who died on March 20 than reconstructing a copy of you on March 21? Why are future simulations of you necessarily less "significant" than current you? This looks suspiciously like a theory constructed specifically to be testable only by death, i.e. not testable to the rest of us.
What looks, at the moment, as the most feasible technology that can grant us immortality (e.g., mind uploading, cryonics)?
I posed this question to a fellow transhumanist and he argued that cryonics is the answer, but I failed to grasp his explanation. Besides, I am still struggling to learn the basics of science and transhumanism, so it would be great if you could shed some light on my question.