Okay, reject his resignation and have him report next Monday.
Uhh... Excuse me, Chief?
There's absolutely no reason to reject his resignation if he's fulfilled his service commitment, which it appears he has. Officers can generally resign their commissions at any time once their commitment is served.
My commitment is/was 8 years on active duty and then 4 years in the reserves. Are you saying that after 12 years I shouldn't be allowed to get out?
"There's absolutely no reason to reject his resignation..."
General principle. Don't get me wrong, let him take his lawyer over with him.