I'm signed up to be a cryonics patient when I die, but yeah, the chances are pretty much nil. Personally, I'll take a slightly diminished bank account and a potentially non-zero percent chance of further life over a zero percent chance, but I won't delude myself into thinking that there's effectively any chance of success here.
Cryonics is ultimately a bet on future technology and future humanity.
Unless you live inordinately long, you'll only be in a position to benefit from that if you are wrong about it being a worthwhile investment. (But right about the technological enablers—just wrong on the socio/legal issues.)
I'd be more concerned with the emotional and mental challenges of being revived centuries hence, which would be considerable to say the least.
Tutankhaman will tell you what to expect when you use cutting-edge technology and preservation techniques in the hopes of some future civilization reviving you.... you'll end up under glass in a Museum. Hell, nobody even TRIED to revive King Tut... you think they'll put much effort into a bunch of anti-freeze saturated popsicles? Seriously doubt it.
That's not a statement of fact, it's a statement of belief. Personally, I think it's highly unlikely that any current vitrification process preserves sufficient information for the patient to be revived. We're nowhere near even understanding what "sufficient information" would be, let alone how to preserve it.
You can flush water pipes with whatever you want and clean and rewater it. A complex organism like the human body - and the brain, we still dont really understand?
Not likely. Maybe not 0 chance in SciFi future, but still not likely.
It IS physically possible to revive cryonics patients--as in the laws of physics would permit it, even if we don't have anything near the technology required, yet. This isn't a bold claim but rather a statement of fact with respect to information preservation of the vitrification process, and long-term storage at cryogenic temperatures, both of which are well studied in the context of things like organ donor preservation.
So if you're claiming that cryonics has "a snowball's chance in hell" of working, then I presume that either you are (1) ignorant of the science, or (2) making some sort of statement about long-term storage prospects or the credibility of the organizations involved.
But neither you nor the grandparent actually made any specific claims.