It will take years to train a fighter pilot true, but given the vintage and number of aircraft, as well as the likely total lack of suitable weapons, I doubt IS wants those Migs to contest control of the skies against coalition aircraft.
While tempting, we should resist the temptation to think of IS as a bunch of mindless fanatics. Undoubtably they have many fighting under their black flag that would fit that bill and then some, that cannot be true for all of them, especially their leadership or else they would not have gotten any near as far as they did.
As such, IS will know that trying to shoot down coalition combat aircraft is effectively an act of suicide, worse, a futile act of suicide as the chances of them being able to even get a shot off are astronomical.
You also have to ask the obvious question of why they are bothering to have Iraqi pilots train their own people rather than for the Iraqi pilots to fly the fighters directly, which would have saved them the bother of having to train up new pilots altogether.
My assessment is that IS do not intend to use those fighters in the traditional manner, but rather use them for some suicide mission (which is why the defected Iraqi pilots are not doing it).
My advice would be for all civilian aircraft to give IS controlled territory a wide berth, as they would make very tempting targets for IS, and with the proliferation of commerical flight tracking apps and software, IS doesn't even need a radar to find, ID and track them.
Needless to say, I would also strongly suggest governments shut down all those programmes and apps as they serve no real useful purpose to the general public, and waiting for an airliner to be shot down before acting is way too late.
Other than shooting down airliners, the other obvious use for fighters would be a 9/11 style suicide attack.
I suppose we are a little fortunate in that there isn't a whole lot of tall commerical buildings left standing in the region, the closest would probably be Dubai and the UEA. There are many military installations, like air bases, but those should be fairly well defended against air attacks, and would also make far harder targets to fly into.
On balance, I still think the greatest threat is to civilian airlines.
