He basically served his purpose of teaching Team 7, but now that they are all stronger than him, what's the point of keeping him around? It would be better for Plot if Sasuke killed him (He'd be a Rogue Ninja after this) and Naruto watches Kakashi's death. Then Naruto realized Team 7 can never be reunited, which was his goal and will finally have the intent to kill Sasuke and stop being emo.