I wonder whether authors really care about people writing fan fiction about their characters and worlds. Surely, it’s just a way for fans to express their love of the author’s creation. Also, all publicity is good publicity, right? And even if your characters are doing things WAY out of character (most of the stuff I end up reading doesn’t tie in with anything even resembling canon), its all fun and games. So unless someone is actively out to destroy your career or steal all your royalties, then I’d let it go. Be pleased that people care enough about what you’ve put into the world to put something of their own in too.
It’s an homage, a tribute.
So suck it up, be grateful, and stop suing people.
