… and a ΔT of 220 °C …
With liquid nitrogen at −196°C and the average temp in the places you suggest well below freezing (A few minutes of googling suggests it wouldn’t be hard to find an average annual temp of −20°C.), I think you could use a more-optimistic ΔT of 175°.
I see what you mean. It’s a matter of what threat you have in mind. I’m thinking mainly of the hostility of a pretty-much intact society to cryonics, and how to take your idea of protecting preserved people by using the notion of “respect for the dead” further, also incorporating the idea of honoring the dead by maintaining shrines/graves, etc.
You’re totally right that if there’s a global depression or civilizational collapse, then the threat of thawing comes more from inability to maintain rather than unwillingness or opposition.
Maybe it would help to split the post, or maybe organize this discussion, to investigate these ideas separately? It seems that engineering speculation about zero-maintenance cryonics is interesting and useful, and that using the “grave” analogy to make cryonics more acceptable and safe from interference is also interesting, but different issues and constraints arise for each of them.