Knight Capital also didn't know what version of software their servers were running, didn't know which servers were originating the bad requests, had abandoned code still in the codebase, and reused flags that controlled that abandoned code (another summary: https://sweetness.hmmz.org/2013-10-22-how-to-lose-172222-a-s...). I'm not sure what you can infer about the risk of a rollback in a less crazy environment.