I am totally just putting this out there and not trying to be annoyingly pedantic, just fyi. The AP rule for capitalization in this case is that this is a title, so if we are speaking of a specific don, it would be capitalized but if just a generic don, it would not be capitalized. So a random don, but Don Corleone. Unless there is a source for mafia style that contradicts this standard rule of course.
In a community totally controlled by mafia, killing the don might lead to some grisly repercussions. Or it could be the start of their downfall. You never know