As a 13th round pick he is far from a lock for the majors anyway. Heck, a lot of first round picks don’t pan out.
Playing pro ball may be a dream, but what this kid most likely missed out on was several years making very little money, playing in the bus leagues.
The ensign needs to remember all the guys that voluntarily left baseball during WWII to enter the military to fight for their country. And the didn’t even have a free education.
He incurred the obligation. Simply tell him to shut up and report on pain of prosecution and brig time. While I was an active Marine I was offered a direct appointment to the Naval Academy. I was engaged to be married and knowing that I could not do both I turned it down rather than making a committment I could not keep. Instead I married, went back to school on my own and was commissioned in the AF. I retired from the AF and am still married after 35 years. Make your committments and take on your obligations wisely and not out of convenience.