Go ahead, sit out and get drafted lower next year for less money. From what I understand, the money he should get is already set/guaranteed and is tied to his draft position. I believe he is holding out because he doesn’t like the way the payment plan is set up. Like it or not, he is only hurting himself by holding out.
If they aren't willing to abide by the terms of a first round draft pick, they should trade their first round pick and only draft in later rounds.