People with narcissistic traits can work towards undoing the damage done to them; but, once you're at the level of a personality disorder it becomes more about coping with the inevitable and continuous fallout. Genetics, trauma, and childhood abuse all come together to create a shell of a human being who, motivated by self-preservation, exists only to consume, exhaust, and expel other human beings.

There are no evidenced treatments, and there is no saving them. They are not capable of changing -- if they were, they wouldn't be (by definition) narcissists. The best thing we can do is teach people to identify and protect themselves from these lost souls.