From A.I. I’d say 10^-3 in terms of flashy stuff like what happens in The Terminator, The Matrix or Twelve Monkeys. Somewhat higher if you mean “broken civilization”, “lost purpose” or the like but A.I. is probably just a stop on the road in that process.

People who are serious about the science of civilization worry about things like “you won’t be able to grow crops in Europe anymore after the Gulf Stream shuts down” or “we run out of critical resources” or “have a nuclear war” or “suffer degrowth thanks to a rollback of globalization” or “we forget how (why?) to fuck” or “can’t solve problems faster than we make them”, etc.

In that case the interesting probability distribution is “how long until a major population/gdp drop”. It is fashionable today to assume that the next “fall” will be terminal for the human race as a whole because we’ll pull up the ladder for our descendants because we burned up the cheap fossil fuels. I don’t believe it. The lesson of history is that the Shang and the Tang and Ming are gone but the Chinese are still here.