> App migrations that may fail and need a rollback have the problem that you may not be allowed to wipe any transactions so you may want to be putting data to a parallel world that didn't migrate.

This is why migrations are supposed to be backwards compatible

https://github.com/flyway/flywaydb.org/blob/gh-pages/documen...

You can certainly bet you followed that advice correctly, now what are the odds you could test a what-if like that in sufficient depth?