It is possible to get a game in a stalemate, most likely due to Claydol. Imagine if both players have 7 cards in hand and each have a Pokemon out, but neither have enough energy. Neither wants to do anything due to decking, so they just keep putting back cards with Claydol. That can happen, just as in a Mewtwo vs Mewtwo matchup.
Should this occur, the judges can decide to hold a Sudden Death if it doesn't seem like the stalemate is gonna break anytime soon.