I have walked away from all my relationships with narcissists. I don't believe a label like that ought to condemn a person and of course, like all conditions that people get labelled with, the individual implications vary. But in my experience these particular relationships were too unsafe to maintain.

I honestly doubt the cancer has anything to do with it. There are reasons that professional licensing boards make it difficult to have a relationship with these people, because they are frought with risks and second-guessing even without the personality disorder.