There needs to be some method to land a GV under the majority of situations. Attacking/defending an airfield really represents the front, so there should be a way to despawn if you can get to a friendly "side" of the battle.
I think each spawn point should be marked to all friendly forces so that at any time, whether you spawned at the point or not, you could drive back to any friendly spawn point and despawn successfully.
It would give defenders on a captured base the opportunity to withdraw (fighting a defensive action to retreat to the despawn point), or, stay and try for the recapture.
The spawn points as they are aren't really all the fair often. Sometimes they put you on impossible ledges, or massive climbs where you'd just as soon despawn as soon as you take a look around. Other times, the enemy has a shorter route to the town for a capture than you do for the defense, so you can't really stop it anyway.
-Soda
The Assassins.