You handle the hypothetical by validating a new environment can be built and bootstrapped. Doing this on a regular basis, either by tearing down and rebuilding

You handle the hypothetical by validating a new environment can be built and bootstrapped. Doing this on a regular basis, either by tearing down and rebuilding dev, or in a separate environment just for this purpose, is not a "nice to have". This same problem exists with monoliths with complicated dependencies, nothing new here. Just like backups, if infrastructure as code isn't tested, it's worthless.