The 50 move rule is still there: either player has the right to claim a draw after 50 moves without a pawn move or a capture. So the game can end then if either player wishes it to (and it almost always will end, because at least one player can expect no better than a draw).

After 75 moves, however, it's not optional, the game has ended. It's still a draw if the game subsequently "ends" in checkmate or a loss on time, though maybe not the players sign the score sheet, move on to the next round, etc.