I think the bottom line here is, there's nothing you can do about them having done that. But if you play them again, you should be on your toes mentally and keep an eye on their positioning.
It's really up to each player to keep track of things like that. Serving order, doubles positioning etc... If you do get rooked on something, and don't catch it right away, there's no mechanism for going back and re-playing or anything. You just have to move on and accept it as done.
I can speak from experience here. I am one of those who's focus is about as far from the match situation as you can get. I am constantly having to be reminded of the score, and once in awhile will take position on the wrong side.