Suppose Bob and I want to bet on whether smarter-than-human AI is technologically feasible. Trouble is, if it’s ever proven that superhuman AI is feasible, that event might overthrow the global economy, making it hard to collect the bet, or at least pointless.

This doesn't preclude a bet. You think money will be worthless in 20 years and Bob doesn't. Bob pays you a small amount of money today in return for you promising to pay him a massive amount in 20 years. Or, just look at long-term bond prices or life insurance prices which should reflect the possibility of money becoming worthless.