Still, it’s possible the Three-Eyed Raven could have just as malicious plans for the rest of humanity, and the Night King was targeting him simply because the Children of the forest protected the Three-Eyed Raven and the Night King hated them.
With him out of the picture, the Three-Eyed Raven can now continue a plan against humanity first started by the Children of the forest.
After all, White Walkers were originally created to destroy humanity remember?