It's getting close to the end of the game and I'm definitely not going to win. Should I break up my hand?

If it is close to the end of the game and you know it is impossible for you to win, definitely consider breaking up your hand. From the other players' exposures, work out what they might be playing and be sure not to throw any tile that you think they may need for Mah Jongg. The safest tile to discard is a joker, as it cannot be claimed by another player. When you're unable to win, the second best option is to aim for a wall game.