Probabilities of basic cryonics tech working are questions of neuroscience, full stop; if you know the basic tech has a tiny probability of working, you must know something about current vitrification solutions or the operation of long-term memory which I do not.
It seems to me that they're also questions of engineering feasibility. A thing can be provably possible and yet unfeasibly difficult to implement in reality. Consider the difference between, say, adding salt to water and getting it out again. What if the difference in cost and engineering difficulty between vitrifying and successfully de-vitrifying is similar? What if it turns out to be ten orders of magnitude greater?
I think the most likely failure condition for cryonics tech (as opposed to cyronics organizations) isn't going to be that revival turns out to be impossible, but that revival turns out to be so unbelievably hard or expensive that it's never feasible to actually do. If it's physically and information-theoretically allowed to revive a person, but technologically impractical (even with Sufficiently Advanced Science), then its theoretical possibility doesn't help the dead much.
I have the same concern about unbounded life extension, actually; but I find success in that area more probable for some reason.
(personal disclosure: I'm not signed up for cryonics, but I don't give funny looks to people who are. Their screws seem a bit loose but they're threaded in the right direction. That's more than one can say for most of the world.)
Getting aging to stop looks positively trivial in comparison - The average lifespan of different animals already varies /way/ to much for there to be any biological law underlying it. So turning senescence off altogether should be possible. I suspect evolution has not already done so because overly long-lived creatures in the wild were on average bad news for their bloodlines - banging their grand daughters and occupying turf with the cunning of the old. Uhm. Now I have an itch to set up a simulation and run it.. Just so stories are not proof. Math is proof.
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