Could possibly just be a handshake deal in the vein of "If we make the Elite 8 we have donors lined up willing to reward you with another million".How can there be clauses in an "NIL deal"? It specifically can't be tied to performance or be "pay-for-play." It's supposed to be for "name, image, and likeness." Unless the clause is something like, extra $$$ for a certain number of instagram followers, it doesn't seem like something like that would be permissible.
Would effectively be impossible to police because you can't really prove that those NIL donors just didn't want to give him more money for his likeness after a great tourney showing.