Reasons why Lee is dead
1. He was shot at point blank range.
2. If he wasn't shot, he was still bitten, there is no cure for that.
3. In a more meta bit, It would be bad writing for TellTale to keep him alive
4. Okay, let's say that he survived: It doesn't matter. There is no chance that he'll track down Clementine again. We might get to play as him in season 2, but no one would like that.
5. Almost everyone had Lee handcuffed, and, he wasn't able to move right before Clem either took the shot, or left him, so why should he after she's gone? If he survived he would be stuck in that one building until he died of blood loss, thirst, or walkers.