Well, even if Magmortar is "dead", the entire deck would have bad matchups to random fire decks. You mention Moltres, what about random Infernape decks? What about Skittles (ho-oh)? What about...etc.
I doubt Magmortar will "die" because it's a good card. It might not be as playable right now, but it would have to be unplayable for it to "die" and it's certainly still a very good card but there is more water entering the format from the new set.
I doubt Magmortar will "die" because it's a good card. It might not be as playable right now, but it would have to be unplayable for it to "die" and it's certainly still a very good card but there is more water entering the format from the new set.