A 'patient zero novel' could refer to a novel that focuses on the idea of 'patient zero' in an epidemic or disease context. It might explore how the first case (patient zero) became infected, the early spread of the disease, and the social and medical responses to it.
Michonne does die in the comics. The circumstances surrounding her death were quite dramatic and had a significant impact on the story's progression. It happened during a major conflict with other characters.