In Season 1 of Game of Thrones, Syrio Forel, the "Dancing Man" who first trained Arya Stark how to use a sword, ran afoul of Ser Meryn Trant. Forel ran off to fight him with nothing but a wooden sword, which was great—except Trant had a real sword. That means Forel almost certainly told the God of Death "not today," and the god was all "yeah sorry, no, totally today." Yet we never saw a body, or even confirmation of his death. That almost certainly means he's alive, right?
Well, maybe. During an interview with IGN, Maisie Williams, who plays Arya, mentioned how the Thrones showrunners squashed her theory that Forel might be the Faceless Man by straight-up telling her, "No, he is dead." Of course, that doesn't mean it's true—showrunners lie all the time to preserve future stories. Plus, as Williams pointed out, Forel might still be alive in the books, because the cool thing about Song of Ice and Fire being so different from Game of Thrones is how one character might be stone dead in HBO's parallel universe, but live on in the original one Martin crafted. That is, if the remaining books ever come out.