Well that would be for a committee of referees to discuss and decide on before making the law. The point is, once you make the law, the case won't happen too often because diving would simply not be worth it anymore. In Italy, for example, they have a three match retrospective ban for deliberate hand balls. Last season, Miroslav Klose accidentally scores a goal with his hand against Napoli, the ref gives it, so Miroslav goes to the ref and tells him that he's scored it with his hand and asks him to disallow it and the ref does.