It's not even a question of him slipping in the draft. Even if he's selected #7 overall next year (the spot he thinks he deserved this year...as if playing for Oakland was some sort of honor :covri:) he can't recoup the lost money from the first year.
The bump in salary he could conceivably earn by re-entering the draft cannot outweigh losing the first year of a top 10 contract. He'd have to go like #1 overall or something, and even then I'm not confident about that without actually doing the math.
He absolutely will lose money by re-entering the draft, there's no way around it.