Looking at the campaign in France of 1940, a lot of airfields were overrun by the Germans, resulting in destroyed airplanes (often by the crew themselves by the way) though sometimes they managed to escape to a new airfield.
So if we overrun an airfield in game, maybe the airplane unit rebases (or get removed from the map if there is no airfield to rebase to) but the unit takes 50 % damage or something like that?