That's a fair question. I was assuming that creatures which can survive full dehydration are so different at the cellular level that nothing less than genetic redesign would do the job, but I'm guessing.
I think part of the problem, too, is that animals who can survive full dehydration, or being thoroughly frozen within and without, are small. We don't often realize just how big humans are, even for land-dwelling tetrapods. We're very large, very active, and very resource-intensive -- certainly there are bigger land animals about today and in our recent past, and very much bigger ones in the fossil record (brachiosaurs, anyone?), but even then we still qualify as megafauna.
The consequences of that size, especially in light of our activity level, are significant. Human physiology is very adapted to dissipate heat well (and our water intake is a big part of that), yet we still routinely have trouble doing it fast enough to avoid ill effects, forcing us to adapt culturally and individually to the problem. We have to conserve quantities (of temperature regulation, of water) at fairly specific levels; our physiology is critically dependent on them.
So, yeah -- if people can be put in suspended animation of some sort (regardless of mechanism), it's gonna have to take our particular case into account. You can flash-freeze a mouse, thaw it, and get biological activity after (they don't exactly go on to live long and prosperous mousey lives, but they do come out the other side for a bit). A mouse is tiny; you can't extend that to a human without different physics becoming relevant. You can dehydrate a tardigrade quickly (just let it do its thing in a low-moisture environment for long enough until it loses enough water) and then leave it sitting until it gets doused again; you can't do that to a human, because we have a lot of water to lose, our bodies fight to hang on to it, our health declines rapidly as we lose even modest amounts, and we proceed straight to death once quantities are insufficient.
If you don't believe in an afterlife, then it seems you currently have two choices: cryonics or permanent death. Now, I don't believe that cryonics is pseudoscience, but it's still pretty poor odds (Robin Hanson uses an estimate of 5% here). Unfortunately, the alternative offers a chance of zero. I see five main concerns with current cryonic technology:
So I wonder if we can do better.
I recall reading of juvenile forms of amphibians in desert environments that could survive for decades of drought in a dormant form, reviving when water returned. One specimen had sat on a shelf in a research office for over a century (in Arizona, if I recall correctly) and was successfully revived. Note: no particular efforts were made to maintain this specimen: the dry local climate was sufficient. It was suggested at the time that this could make an alternative method of preserving organs. Now the advantages of this approach (which I refer to flippantly as "dryonics") is:
There is one big disadvantage of this approach, of course: no one knows how to do it (it's not entirely clear how the juvenile amphibians do it) or even if it would be possible in larger, more complex organisms. And, so far as I know, no one is working on it. But it would seem to offer a much better prospect than our current options, so I would suggest it worth investigating.
I am not a biologist, and I'm not sure where one would start developing such a technology. I frankly admit that I am sharing this in the hope that someone who does have an idea will run with it. If anyone knows of any work on these lines, or has an idea how to proceed, please send a comment or email. Or even if you have another alternative. Because right now, I don't consider our prospects good.
[Note: I am going on memory in this post; I really wish I could provide references, but there does not seem much activity along these lines that I can find. I'm not even sure what to call it: mummification? Probably too scary. Dehydration? Anyway feel free to add suggestions or link references.]