Hi -
I also can't quite say what the opposite of NPD might be, but did once read a great article that described personality disorders generally, in comparsion to more specific mental illness diagnoses.
The metaphor used was how fat appears in piece of meat (as I write it, I realize its not appetizing, but I think it conveys the idea): with a straight mental illness (of all sorts), its comparable to the outer layer of fat that may need to be trimmed off, etc. but the underlying core (or personality) is in pretty good shape. With a PD, the fat is marbled throughout -- the personality is intermixed with the disorder, and it is not straightforward to fix.
In otherwords, even severe MI, once treated partially or completely, may liberate a fairly well adjusted person within. PD on the otherhand may never even get to the point of treatment, since the person may not even consider their condition to be a problem, and the the separation of problem/person may not be possible with conventional MI treatments such as medicine or therapy.
I was first intrigued by this article since I was suffering from major depression and had a sibling with schizophrenia...yet was fairly certain my father had some undiagonosed disorder...and only in couple years after that did I really understand that it was my N-mother who likely has the major personality disorder. And I consider her condition to be much more intractable than the worst I've seen in my brother's major MI. In otherwords, despite his occasional delusions/symptoms, he manifests what we'd all consider 'good' human qualities. With my N-mother, I rely on faith there is good in there somewhere, but it is really hard to see as it is interwoven with genuinely bad actions.
BG