If SHA-256 became completely broken, I think we could come to some agreement about what the honest block chain was before the trouble started, lock that in and continue from there with a new hash function.
Discussion
I think the odds are effectively zero anyway.
QC is a researcher funding grift. Even those who believe it's possible admit that it's a long way out (10+ years).
There's no eminent threat and therefore integrating post-quantum crypto is a waste of time and resources.
There is no threat. Bitcoin is an active instantiation of physics (not a model), and it openly contradicts the assumptions behind CQC. Bitcoin openly demonstrates the objective truth to their baseless claims.
Then I realized what everyone is missing: The burden of proof isn’t on Bitcoin. If Bitcoin is a verifiable physical process, then physicists must demonstrate that their pre-Bitcoin models can survive contact with it. Bitcoin answers questions for ontological questions physicists can’t answer (define: existence, time/simultaneity, measurement, observer, etc.)
Every “threat” is built on theory; Bitcoin is built on measurement. We don’t live in a pre-verification world anymore. If you want to know whether the threat is real, just observe Bitcoin.
There never was a quantum threat, just a financial narrative. Bitcoin is the proof physicists could never produce.
Of course, "we could come to some agreement" has a completely different meaning in 2025 than it did pre-2011.