If they win the bet against you, you'll both be dead by definition of the bet. Therefore the bet doesn't make sense and shouldn't be taken seriously.

Something like https://longbets.org/ maybe? The funds get held by a third party, and go to the winner's choice of charity rather than to the winner.

It could go to the estate.

You could bet in Bitcoin. If the quantum computer doesn't exist, one person gets it. If the quantum computer appears that can break the Bitcoin digital signatures, well, then the Bitcoin is worthless.

For some reason, this reminds me of the ding dong who bet bitcoin would hit a million dollars, immediately lost, then claimed he was the real winner because it proved people were interested in bitcoin.

That bet was the least interesting thing about John McAfee.

I believe he said he would eat a ding dong too.

I'm sure someone smarter than me can come up with a way of making bitcoin quantum-safe with a soft fork.

Of course, the addresses created right now would still be at risk.

Encrypt a file with “2000s era cryptography” (not too sure what that would be). The file contains instructions on how to unlock a sum of money.

Ok, but how do I make money from that?

One of the University of Iowa B schools runs a futures market that'll let you bet on predicted event outcomes

https://iem.uiowa.edu/

https://en.m.wikipedia.org/wiki/Iowa_Electronic_Markets

Problem with long term bets is time value eats away at escrow. But sure, come back in 20 years and we'll settle up at whatever a week's worth of US median salary is. (For specifics, 2000 era crypto is 1024 bit RSA. I'm not betting against a conventional supercomputer factoring such coprimes though.)