I have noticed that even if all structures at airbase have been destroyed, aircraft can still roll out of it. Now, if people want to risk getting vulched while taking off from a base like this, fine. Unfortunately, people will see paras come in, then get in a plane, "drive" around and shoot them all!
Perhaps there could be a structure, or a small number of structures, like rivetments, along the field that represent parked aircraft. Once these are destroyed, no aircraft can come from that airfield.