If you are travelling on a Rebate or ID ticket you are effectively " standby", if they accept you and you board, then a whole bunch of "confirmed" passengers arrive you can be off-loaded, applies even to duty travel. Now, if you take off and the plane diverts you would normally be given the same privileges as any passenger as the airline has a duty of care, on the other hand, if you never got airborne and were simply off-loaded due to no seat, then in most cases you have no rights for compensation, they will simply put you on a wait list for the next flight and the accommodation is down to you. Normal passengers are subject to the delay compensation, but not ID travel.. in practice the gate staff will give you a food voucher if the flight is just delayed say 6 hrs, but not Hotac.