Hopefully you are a proper software shop and you do more than just run test suites to see if something is working :)
And if you discover that "hey, changing X broke Y but we didn't catch it before", then obviously you rollback the change and start working towards how you can prevent it in the future.
Of course there will always be fuckups, but this strategy wouldn't make it harder/easier to rollback those changes.
Right, but it removes the opportunity for a second dev to see subtle but catchable issues that are the most likely to get missed in isolated testing by dev/first level QA. Race conditions, improper use of lifecycle hooks, scaling issues, etc.
And good luck getting a SOX auditor to give this process an OK!
And if you discover that "hey, changing X broke Y but we didn't catch it before", then obviously you rollback the change and start working towards how you can prevent it in the future.
Of course there will always be fuckups, but this strategy wouldn't make it harder/easier to rollback those changes.