My understanding is it's generally un-curable since it's such a deeply rooted and ingrained coping mechanism for the ego. Like an addiction. But if I had to guess, someone would probably have to deeply work on true self-compassion (a lot of narcissists are, internally, extremely self-critical, if I understand the condition correctly) and build back from near zero. Sounds really difficult.
It's intractable. There is no solution except teaching people how to identify and protect themselves from narcissists, or institutionalization.
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.
There's no incentive for them to change. If they can use people and then discard them for new supply, maintaining their power over people with manipulation and games -- then why change? Change would involve becoming vulnerable, giving up their means of power, and confronting their harmful actions.
