I see this happen all the time with members of the MXG here in Korea. Usually the FSS just extends their DEROS, and the MXG middle management (junior NCOs) in charge of those young airmen don't mind, because they keep their "bodies" around.
I saw a guy PCS 3 months after his original DEROS, and only after a high-speed Top-3 buddy of mine overheard his story and started advocating for him. Then we got to watch everyone act all surprised: "WHAT??? THAT'S HAPPENING HERE???" GMAFB.
When overseas on a remote, playing chicken with the FSS doesn't end well. It **SHOULD** result in people getting fired, but leadership on that side of the flightline has been broken for so long, you can't expect much.