Erm, yes, they can and will.
Depending on where you quit even in ROTC it's either pay the F up in cash, or enlist and "work it off".
I had a guy in my platoon at 3/75, who was going into his junior year and basically decided that being an officer wasn't for him. Military? yes... but the whole officer bit just didn't suit him.
So, he enlisted to pay it back, came to Regiment, ended up doing 6 years, shitton of deployments, and is now out. Great Ranger, just a personal decision he made knowing the consequences.