The Night’s King isn’t even in the books, is he?
Or, rather, so far, in the books, the Night’s King was a Lord Commander of the Night’s Watch (and probably a Stark, to boot) who went rogue during the Age of Heroes without any direct connection to the Others.
The tv series has shown more of the White Walkers (Others) than the books have, and the Night’s King might be an invention of the tv series to put a face on the White Walkers, and the books may never show an identifiable leader of the Others.
Now Martin has said that the stuff we know about from the Age of Heroes is mostly legend, and that those stories (Lan the Clever, Night’s King, Bran the Builder) may be embellished and not entirely true.
The sequel series is going to be set during the Age of Heroes, so it should be interesting to see how all of this goes down.
In the supplementary material for the tv series, they have said that GRRM told them that “Hodor” means “Hold the door,” so we can assume that Bran’s ability to change the past is from Martin himself, so it’s probably safe to assume that it will be important later on in both versions. I’m thinking that Bran will probably use his time travel abilities to defeat the Night’s King and White Walkers.