I expect cryonics to basically work on a technical level.

Even given this, I would doubt:

Most of my probability mass for not seeing them again is concentrated in Everett branches where I and the rest of the human species are dead,

E.g. what about the fact that cryonics organizations have the financial structure of precarious defined-benefit pension plans during a demographic decline and massive population aging, save that those currently receiving pensions can't complain if they are cut?.