Well, that's a toughie!
You already have a successful carreer path mapped-out. For what it's worth, I'd suggest you steer clear of "arty- Farty" "soft" subjects....Even stuff like an MBA is tarnished.
A solid, science-based degree would seem the way to go, you would need to match the degree to your own interests and affinities.
Something like the Open University courses may be a possibility to continue working and study mostly at your own convenience.
Chucking a stable employment at this stage of your life would be foolish. I don't see the Air-travel industry regaining it's former profitability for a long time yet. (oil prices and world recession have killed the holiday/charter market)
just my take on things, be interested to see others' opinions.