To answer your Q's:
1. Lots of options, all costly, and in my opinion, all unattractive.
2. No bridging package available.
3. Why does he (or she) want to leave? He has obviously done quite well up to now, but has no real experience of military life/operational flying upon which to base a decision. The grass is not always greener, even in the light of a longish and frustrating hold. He will be viewed by the airlines as a beginner, but will already have his wings - no mean feat. I would suggest he sticks it out - he will certainly enjoy the flying more than the airlines. Most airline pilots will tell you that there is very little 'real' flying - and there is always the opportunity to become a civvie pilot later.
As Del said - there may be more to the picture than is first apparent...