The Chronicles of Narnia: The Last Battle?

Now that you know that they did die, (not only Peter, Edmund and Lucy, but Eustace and Jill and Digory and Polly as well), I will just answer the question about living forever in Narnia. they do lived forever in Narnia, but in a new one, created by Aslan. the old one had been destroyed simply because there had already been a lot of chaos in the old one. I suggest you read the Last Battle for more information.