The thing about this bet is you don't have to pay until 2048 whereas I have to pay as soon as it happens and accounting for savings rates the bet will cost about a dime a day.
In my experience were really bad at figuring out when something more than about 5 years out is going to happen so 10-20 years is much worse than a coin flip. That's partially because we don't know what second and third order problems could come up, but also because interest/investment could change rapidly. For example, if some other probabilistic method of factoring primes (or even NP complete problems!) were discovered that would massively reduce funding for QC.
And yeah, there's a time value of money, inflation, repayment risk, and a zillion things that vary the value of a long term bet's payout, but at ~3-6%/yr they don't affect it by more than a few factors of 2. The risk of having all the world's stored encrypted data decrypted after the fact makes even a miniscule risk that QCs can break RSA or other encryption too big to accept. Those scale by many factors of 10.
