It doesn't matter whether anyone writes one drabble's worth of fanfic about your work, OP. As soon as someone other than you reads a single chapter out of your manuscript - and dozens of people will, your agent, your copy editor, your story editor, your typesetter, etc. - then your characters will be in someone else's head doing things that you never imagined them doing. You see, literary characters don't exist on the page; they exist in the imagination of the reader. And once they're there, they're made up of that dirty, filthy reader's thoughts and emotions and impulses, not yours. You no longer have any control over what they do and say once they're there; all you get is that one shot, on the page, to get as much of your concept of them across as you can.

After that, it's like an adult child leaving home - you just trust that you brought them up right and hope for the best, because there's no telling what they'll run into in a dozen other brains. And, like adult offspring, if you think they're not going to fuck out there, then you need to adjust your expectations.