J.C.
Yes - it's his to use but once you are termed, you can't use it any more. So, if he wants to use the full 2500, he better get going now. I don't think it is morally wrong at all. It's a risk both sides take. You could use the full 2500 on January 1 and quit on January 2 or they can term you in November and if you haven't spent anything, you lose it. I'd tell him to use it up and fast.
And yes, he could have spent the 2500 on January 1. Assuming it's all for medical. For dependent/child care expenses, you only get out what you put in.