"Moriarty slipped up, he made a mistake..."
Oh, no. He didn’t.
He told Eurus about Molly.
In those 5 minutes, he told her about the things that would drive Sherlock out of his mind. And of course, he also told her about the person who mattered the most, giving her the opportunity to play with Sherlock’s emotions.
Thus, even after death, Moriarty managed to “burn the heart out of him”.