The very last book in the series "The Last Battle" is basically an account of the Narnian apocalypse. The world ends, Aslan the Lion-Christ winnows the wheat from the chaff and all the good creatures go to a heaven Narnia for evermore.
C.S. Lewis was not only a good story-teller, but an interesting theologian. He makes heaven to be a "realer" version of Narnia (and likewise the earth's heaven is a realer version of earth.) One of the characters, a professor, references Plato in an aside. The mundane Narnia and Earth are called the Shadowlands. The children get to visit a heavenly England.
This is an intriguing take on the Christian idea of eternity. Nevertheless, even as clever a heaven as Mr. Lewis' perforce seems rather insipid to a Buddhist. It's all green grass and lolly-pops, for sure, but it's still all conditioned isn't it? The idea of conditioned existence prolonged for ever, even in a perfect Narnia, has a horrific edge if you think about it.
Notching down from the metaphysical a bit; I've commented before on Lewis' use of language and I'd like to cite one example. Remember this is from a children's book written in the fifties.
The children are about to leap into a churning waterfall in the heaven-Narnia;
"Isn't it wonderful?"said Lucy "Have you noticed one can't feel afraid even if one wants to?"
"By Jove, neither one can." said Eustace after he had tried.
That kind of syntax must be what comes of teaching Latin and Greek in the schools.