The bottom line is that there is nothing to worry about for many years or even decades.

Out of all the various parts of bitcoin, the bit which is the most vulnerable to quantum computers (via Shor's algorithm) is the elliptic curve itself, which means an attacker being able to take a public key and calculate its corresponding private key. Reverse engineering from addresses (rather than from public keys), mining, and many other parts of the protocol are less vulnerable because they use various hashes, which are far more quantum resistant than the ECDLP.

So at some point in the future we will likely fork to some new quantum resistant cryptography before quantum computers pose a serious risk. We don't need to make any decision regarding this for years or even decades, and indeed, making such decisions now would be a mistake given the entire field is in its infancy and any system we chose today would likely have been replaced by something else by the time it was actually relevant.

Don't forget that in such a scenario then almost all the encryption currently used across the entire internet will similarly be broken, including everything to do with the fiat banking system.