Before I get into the weeds with links ITT, to be clear, if QC does reach a hypothetical power that would threaten private key security, a BTC fork seems to be the general consensus for the main possible fix.
yes, that is how cryptography has been its entire lifetime. ever since it was perceived more than 2 thousand years ago (before computers), every cryptography method had an expiration date when they become obsolete and are replaced by newer ones that are stronger before the same thing happens to them too.
as for ECC and SHA256 (the two main cryptography used in bitcoin), i don't think they would become obsolete anytime soon but when they do, Bitcoin simply upgrades to newer and stronger algorithms.
However, the problem with the possibility of the emergence of quantum computing that can quickly crack existing digital access codes, including our secret keys to cryptocurrency wallets, is still very real. Response protective measures, even if they appear and are publicly available, may be late for some time, and therefore many people can be very badly affected financially. This problem is very serious and should not be underestimated. When quantum computers arrive in the hands of attackers, it will be too late.