There's nobody running against him so, unless the Republicans field a candidate who must file by 6/30, the job is his without an opponenet to face in November.
I'm not sure I understand your second paragraph. If DUMC said there was no rape, but NCU said there was, which apparently they didn't, Duke would be chastised and vilified. But if UNC hospital agreed with Duke's findings, then Duke would be off the hook. So, how would going to UNC shore up Mangum's story? I'm not following your reasoning.
Not to shore up her story, but Nifong and the Durham PD knew that the Duke medical report would not support the sensational allegations she was making. Miraculously, she appears at the UNC Hospital the next day (we don't know what they said, other than Crystal telling them even different stories about what happened).