Ok, so Law can't hurt Regulus, while Regulus can't hit Law for the first moment. So the whole wincons for this match is:
For Regulus: He gonna stalemate Law into fighting him for days (A thing he would't have any patience, but he don't have any choice) since his stamina is basically infinite, he would need to wait until Law is tired enough so he can hit him.
Law: He can't hurt Regulus, so he would need to figure out his Authority. He could probally understand the time stop aspect, but not that his connect to his wifes. At least, he would't have a good time doing that. Considering they would be fighting for days, Regulus wives have the chance of dying of starvation, since I doubt any of them can find much food in a forest, or just die due to getting caught in the crossfire of the fight. So Law can wait until Regulus wives dies, and he can kill Regulus.
I think this is It. Someone can correct me If am wrong or provide another scenario.