Enlisted folks serve rather like politicians: they are term-to-term, reenlisting every 2, 4, 6, or whatever years. Officers get commissioned, usually have a minimum service contract (8 years for me) that might allow part of it to be in the reserves, and then can resign their commission, but as far as I know they cannot resign during an assignment, only in between assignments. Assuming Lieutenant Watada is an O-2, he's probably got between 2 and 4 years of service in and wouldn't have completed his service obligation yet.
My guess is that he's going to face more than a slap on the wrist, as the DoD is going to make an example of him.
Edit: And yeah, ditto what MobBoss just posted - Stop Loss would get him even if he didn't have any remaining service obligation, so he's stuck either way. And screwed.