If there was clear evidence of Derby cancelling the fixture in order to gain an advantage then I would expect the game to be replayed, but Derby to receive a fine and 3 point deduction.
However, I can't see how that is ever going to be proven conclusively, there will always be just enough doubt that the fa will have to give them the benefit of the doubt.
Failing a whistleblower from within Derby county I can't see it going any further.