Courts know how to deal with cases where change of ownership (or another tort) is not reversible. It's as simple as if I promised you to pay you $100 for the dinner in your restaurant, ate the dinner and then never paid because I had no money. Obviously I was perpetuating fraud - I knew I have no money and still ate. But I can't return you the ownership of the food I ate. So the court would just assign just compensation (via various mechanisms) for fraud in that case, and maybe something on top to punish me for what I did. The only problem would be collecting it may prove impossible in this case.