This is why SHA-3 exists. If it starts looking feasible that SHA-256 is going to be broken, we already have alternatives. We've already seen TLS et al switch from hashes like MD5 and SHA-1 a few years ago. Pretty much all the other systems have systems in place to migrate in case one part of the validation system is cracked. Bitcoin doesn't, and given the fractured state of the community, having a migration system would be difficult at the very least.
