The world has already migrated through so many past now-insecure cryptography setups. If quantum computers start breaking things, people will transition to more secure systems.

In HTTPS for example, the server and client must agree on how to communicate, and we’ve already had to deprecate older, now-insecure cryptography standards. More options get added, and old ones will have to be deprecated. This isn’t a new thing, just maybe some cryptographic schemes will get rotated out earlier than expected.