As says in the tin. Let's imagine that he doesn't develop the illness that eventually killed him, and instead he dies only in 1700, at 70 years old (his brother died almost being 68, so I don't think it would be too far fetched). Of course, he remains without a legitimate child, but the Duke of York (who IOTL would already be king James II) still have a son born from Mary of Modena. Would there be a plot to depose Charles and expell James and his son from the country? If not, how would Charles deal with the now increased fear of a lasting Catholic dynasty?