You are in a difficult position if your wife does not want to get help. IF someone is narcissistic a main trait in their personality is the lack of empathy in addition to feeling superior to others.
Another hindrance is the fact that personality disorders are never really cured. The individual can learn to manage their behavior to an extent if willing. If that is her primary diagnosis also insurance does not pay for treatment of personality disorders w/o the existence of another co existing disorder.
Having been the bearer of these news, you have limited options. One is to continue to encourage her to seek help (family counseling with another therapist) two, setting some kind of an ultimatum, last resort which you have already mentioned - leaving.
Try to find out from her where she believes the relationship is heading and if there is anything she would be willing to do to make things better. After all, a relationship is made up of both partners and you cannot be the only one trying to work things out.