He'd probably get $1.5-$2MM next year at Notre Dame. If the confidence level is high that he'd be a Day 2 pick in the draft, that's about what he'd get per year on a rookie contract. Maybe he could get a couple of those seasons guaranteed, so if so, locking in $3-4MM in guaranteed money could be smart, especially with a potential injury risk next season.
The risk of leaving early is that he could feasibly be drafted much lower. Then he'd be foregoing the N.I.L. money he'd have made for less money in the pro's with no guarantees, and basically have to hope that he's in a situation where he can earn a good second contract.