We do have the entire build history stored on our systems but we don't have a way to let developers roll back the active build right now. This is something we need to add. In the meantime, you can push the older version on the same branch and a patch that reverts will be applied.
Thanks leafo! I can see how that would work :) the main issue from that approach though is that I would have to keep a local history of all builds published on itch.io and make sure I never ever modified them (or lose them). Out of curiosity, do you have an estimate on when would that roll back feature be available?