Re: even if the chance of cryonics working is only 1%
0% is a big call. Yes we know we couldn't revive those people now. If we could revive them now, we wouldn't be freezing them in the first place. But how can we be 100% confident about all the possible medical and technical advances between now and the point when someone accidentally trips over the freezer cord? Even if it's true that the brain is destroyed beyond any possibility of repair by any future civilisation (which I don't think is a certainty), isn't it at least possible that someone in the future could cut it in to very thin slices, scan the whole thing with an electron microscope, simulate it in software and stick it in a robot body? It seems outlandish but I don't see anything there which is fundamentally impossible. In fact not only is it theoretically possible it's actually being done right now (but only for flatworms).
You might think it's unlikely to ever be possible, fair enough. You might think that even if it becomes possible, a future immortal civilisation will have enough overcrowding problems that it won't see any value in reviving 21st century brains, fair enough. But those are reasons why it's unlikely, which I fully accept (hence 1%). Not reasons why it's impossible.
I doubt there's a legal definition of death other than "has been declared dead by a doctor". Even if there was a legal definition, if someone recovers and is walking around talking then it doesn't really matter what the law said does it? A hundred years ago we'd have said, if your heart has stopped beating, you're dead but now there are loads of people walking around whose heart had at some point stopped. In another hundred years, declaring someone dead just because there had been a lack of blood to their brain for a few hours might seem absurd.