Certainly add "uncertain existence" immediately and then when it really appears the person is a fiction, put address a one week Disproven Existence notice to G2G. That alerts everyone that this is going on, and after a week, the disproven existence badge can be added. At that point a project must be one of the PMs. While another project which wishes to can be the PM, projects like England often feel they have enough on their plate and are happy to turn it over to the Disproven Existence Project at that point.
Two features of Disproven Existence are that (1) the person is disconnected from other profiles, so he doesn't appear in anyone's family tree, and (2) words are added to the biographical narrative stating why the person is believed to have never existed, and links to the profiles the person used to be connected to. That means if any facts about the person are discovered in the future, he or she can be reinstated as a real person!
Jack Day, Project Coordinator, Disproven Existence