So to answer your question if a college athlete underperforms the 3rd party can end the NIL arrangement only if the contract or state law allows it.
Well, assuming a contract does exist, then how can the student athlete be allowed to leave without punitive damages? I mean, I am assuming he is over 18, and thus any contract he signs is legally binding. Breaking said contract might not prevent him from entering the Portal, per NCAA rules, but most certainly there could be other damages that could be enforced.