The negligence on this migration sounds breathtaking: they have a four-nines availability requirement and decided to do a big bang migration with what sounds li

The negligence on this migration sounds breathtaking: they have a four-nines availability requirement and decided to do a big bang migration with what sounds like virtually non-existent, or at least grossly inadequate, testing and no ability to rollback. People, often contractors, do get fired all the time for buggy code. Companies get sued for buggy code. However, the issue here isn't really the code, it's the management of the project. Bugs happen all the time, and at every stage, during development which is why large migrations like this need to be done very carefully with ridiculous amounts of testing and rollback procedures. Even when you think you've got everything covered, it's amazing the things that can go wrong on go-live.