First, let’s hope the captured pilots are making mistakes in their training instructions.
Second, they may be able to fly them somewhere once or twice, but to have an Air Force, they will need to maintain. They probably excuted all the maintenance personnel.
My Special Forces son spent 4 months at helicopter maintenance school, so he could manage a fleet of 6 or 8 helicopters. My other son who worked for an avionics company said 4 months was not enough for him to repair them, but only to communicate with the workers and know what he was ordering for repairs. Fat chance that ISIS will be able to do that.
They have over $6 billion dollars and counting. You can hire mercenary maintenance personnel from the third world (MiGs are everywhere) for $20,000 a piece all day long.