My estimate of the core technology working would be "it simply looks like it should work", which in terms of calibration should probably go to 90% or 80% or something like that.

Estimates of cryonics organizations staying alive are outside the range of my comparative advantage in predictions, but I'll note that I tend to think in terms of them staying around for 30 years, not 300 years.

The weakest link in the chain is humankind's overall probability of surviving. This is generally something I've refused to put a number on, with the excuse that I don't know how to estimate the probability of doing the "impossible" - though for those who insist on using silly reference classes, I should note that my success rate on the AI-Box Experiment is 60%. (It's at least possible, though, that once you're frozen, you would have no way of noticing all the Everett branches where you died - there wouldn't be anyone who experienced that death.)