I guess this would be my attempt to answer your first question: articulating what I meant without the phrase "level of death".
My answer to your second question it tougher. Somewhat compelling evidence that whatever I value has been preserved would be simultaneously experiencing life from the point of view of two different instances. This could be accomplished perhaps through frequent or continuous synchronization of the memories and thoughts of the two brains. Another convincing experience (though less so) would be gradual replacement of individual biological components that would have otherwise died, with time for the replacement parts to be assimilated into the existing system of original and earlier-replaced components.
If I abruptly woke up in a new body with all my old memories, I would be nearly certain that the old me has experienced death if they are not around, or if they are still around (without any link to each others' thoughts), that I am the only one who has tangibly benefited from whatever the rejuvenating/stabilizing effects of the replication/uploading might be, and they have not. If I awoke from cryostasis in my old body (or head, as the case may be) even then I would only ever be 50% sure that the individual entering cryostasis is not experiencing waking up (unless there was independent evidence of weak activity in my brain during cryostasis).
The way for me to be convinced, not that continuity has been preserved but rather that my desire for continuity is impossible, does double duty with my answer to the first question:
[Unambiguous, de-mystifying neurological characterization of...]
whatever routine occurrence it is that supposedly disrupts my brain state as much as a destructive scan and rounding to the precision limit of whatever substrate my copy would be running on.
In June 2012, Robin Hanson wrote a post promoting plastination as a superior to cryopreservation as an approach to preserving people for later uploading. His post included a paragraph which said:
This left me with the impression that the chances of the average cryopreserved person today of being later revived aren't great, even when you conditionalize on no existential catastrophe. More recently, I did a systematic read-through of the sequences for the first time (about a month 1/2 ago), and Eliezer's post You Only Live Twice convinced me to finally sign up for cryonics for three reasons:
I don't find that terribly encouraging. So now I'm back to being pessimistic about current cryopreservation techniques (though I'm still signing up for cryonics because the cost is low enough even given my current estimate of my chances). But I'd very much be curious to know if anyone knows what, say, Nick Bostrom or Anders Sandberg think about the issue. Anyone?
Edit: I'm aware of estimates given by LessWrong folks in the census of the chances of revival, but I don't know how much of that is people taking things like existential risk into account. There are lots of different ways you could arrive at a ~10% chance of revival overall:
is one way. But:
is a very similar conclusion from very different premises. Gwern has more on this sort of reasoning in Plastination versus cryonics, but I don't know who most of the people he links to are so I'm not sure whether to trust them. He does link to a breakdown of probabilities by Robin, but I don't fully understand the way Robin is breaking the issue down.