What if the prophecy meant that in order for either one of them to die, it had to be at the hand of the other. So because Harry wasn't killed by You-know-who, he was now immortal. He would forever be "The Boy Who Lived."
Then again, if Harry hadn't been killed by Voldy, Voldy himself would also be immortal, because the last Horcrux wasn't destroyed. Not really a rosy future, if you ask me.
I'm wondering more about what will happen with the new movie, Fantastic Beasts and where to find them, but I always thought the prophecy was very wonky anyhow. It doesn't sound to me as though one has to kill the other... uh.
So because Harry wasn't killed by You-know-who, he was now immortal.
He would forever be "The Boy Who Lived."