If you try to sue someone for copyright infringement and they demonstrate that what you're claiming is infringement is solely the result of model output, you're

If you try to sue someone for copyright infringement and they demonstrate that what you're claiming is infringement is solely the result of model output, you're going to be out of luck, and honestly I don't think that's a problem - if your creation is so derivative that a model produces it via a reasonable prompt it probably doesn't deserve protection. Using prompt interrogation on a specially fine tuned model in an attempt to end-run a reasonable copyright is a different matter, but I don't think that'd be worth the effort for anyone to actually do. If a copyright precedes the existence of a model, the model was trained on that code and someone distributes code from the model that is a near-verbatim reproduction, that's a different story (in large part because getting that near verbatim reproduction would probably require willful intent rather than just being accidental)