A vulnerable system that can't be patched shouldn't be in a position where that vulnerability can be exploited, if it's mission-critical. If it's mission-critic

A vulnerable system that can't be patched shouldn't be in a position where that vulnerability can be exploited, if it's mission-critical. If it's mission-critical, it's vulnerable and can't be patched, and has to be exposed, then it's not fit for purpose and has to be replaced, or have a replacement (i.e. a backup) on stand-by. Yes, restoring a backup requires effort. But surely less effort than losing the data altogether.