"A terrorist attack of far less complexity than 9/11 etc could easily shut the RAF down."
Without wanting to sound blase, I would suggest that shutting down a permanent RAF base on a full time basis is a significantly challenging task, which would require more than either the hijacking of 5 x airliners, rediverting them and then crashing them, all the time without ADANA being called.
Perhaps you could point the threat out which has potential to wipe out all of our home stations at once?
I am rather boring, but I'd rather see money spent on kit, and not on surplus infrastructure if possible. We're in the business of closing with, and killing the enemy and not estate management.