From what I've read Chesko's response to FNIS being a part of the fishing mod was "Valve told me it was OK because it was publically available and it was also free..." he then did the right thing and pulled his mod from the paid store. However, there's almost nothing that can be done if your mod is being used as part of a paid mod, because you basically allow Bethesda to poke, prod, exploit, sell, eat, or touch inappropriately your mod as soon as you make it public. So as long as Bethesda is getting a piece of the pie, I'm not sure you have any real recourse outside of potentially long and expensive legal battles if you find a mod using parts of yours and you say "hey, I don't like that..." and the cancerous paid mod author says "tough crap...I'm not pulling it..."
