Ted can't really fight (or at least he couldn't in that condition), he can't lockpick, he doesn't know all of the things Joan and Sherlock do that might've allowed him to free himself. But he can be very, very stubborn, and he can have faith in people. He doesn't quit. Which might've saved his life.

He smiles at her leaning her head against him, just standing there for a moment. Being grateful that things didn't go as bad as they could've.