There are ways to work with NPD people, besides what NIK said. It's some of the most difficult conversations I've had in my life because I have to plan them word for word, but it can be done, believe it or not.
And yes, like NIK says, eventually they tire of a person and find another.
One way I proceed, because we are tied by children, is to choose my answers or points of conversation carefully and when you can be open ended, it's wise. I sometimes do this with DD, who is entering puberty and dealing with the loss of her father every day from what he did, so it helps there too, and she has signs of some NPD there also.
Anyway...the gist of it to never, ever demand and also never, ever show feelings. If you have emotions, wait until they pass to be in contact, for a true NPD person will never forget the emotional part and may hold it against you...as Nearly Exh does.
The other part of this part of it is to be open-ended in response. By that I mean, when you reply or have a question or need something answered, I've learned I get further by giving a kind of multiple choice question. Then, it's his choice in how he replies and he can feel he has some control in his part of whatever, which is part of the NPD game. If you give yes or no replies or "it has to be this ways", over time this builds resentment and doesn't lead to anything good-often shut down.
This is one of my favorite subjects and though I am no counselor, the two I've had said these are good methods. It's kept drama down and gotten us past issues more quickly. He said once, too, "You've changed". I haven't really, but I've changed how I interact with him and play almost a little game with him. I've known him a long time and can generally peg his answers ahead of time, but this is a way to be amicable with NPD that took a while to learn.
I have several other relatives with it and this works there, as well as turning the conversation to them if it gets too personal or difficult. Ashland 13
You gave me nothing and now it's all I've got - Bono
A person is a person, no matter how small. -Dr. Suess
Perserverance and spirit have done wonders in all ages.