I do not think that Nifong was driven by the amount of his future pension. I think that Nifong was consumed by the fact that Freda Black might beat him out once again. I think Nifong was willing to do anything he could during the primary season to prevent her from ousting him again.
I think that you are absolutely right that the primary motivation is to hang onto the DA position. The pension thing is simply an added element in the equation, but one that I hadn't thought about until the article.