This is something that I would be concerned with. If you have a multiplayer game like Runescape, and have CD on the servers, introducing a bug that causes corrupted data may be able to be patched quickly, but in that hour a lot of players could have been given items that they shouldn't have had. Then you have to distinguish which got the items properly and which didn't, and have processes set up to make those kinds of admin changes to the prod db
Goes without saying that you deploy to an identical test environment that duplicates the entire stack, with realistic test data. Automated testing protects from regressions, manual testing for the rest.
Some stacks are quite complicated, involve various kinds of mobile devices with different app versions, custom hardware, offline functionality. It's just that not all systems are easy to replicate. But that's another problem.