I think that once Grace won the game, she was a recipient of Mr. Le Bail’s fortune and curse. It would explain the nod we see him give her when he briefly appears in his chair. I also believe that’s why Alex didn’t explode until she took the ring off. When you marry someone, you become your own new family unit. Alex existed in that moment as part of the Le Domas family, and also as part of his family with Grace. Once she removed the ring, she broke their bond, and he was no longer part of her family. He was a full original Le Domas, and therefore eligible to die.
