Nyx saves Luna in Altissia and that saves us all from heartbreak. He never wears the ring in the first place so that's why he survived, killing Drautos with his own strength. So after the world is saved, the princess of Tenebrae marries her one true love.

+Nyx weirded out by the fact that he's going to be a prince but he only cares about being by Luna's side so it's ok.