Maleficent says what she said because whatever she does to Snow and Charming whether it be revenge or not it is still not going to bring Daniel back. That is the hole in the heart that cannot be filled. Even if she wins this fight, what does she really win? Regina will still not have Daniel. That was what Henry was trying to tell her before she ripped his heart out. She needed to get over it and move past it in order to heal herself. A famous man once wrote before seeking revenge on another you first must dig two graves.