CBS radio reports it was hit by an RPG, so flares wouldn't have helped a bit. From talking to a former Army test pilot, and an ex Marine CH-46 pilot (similar design), they are vulnerable if hit in the right place. That dual rotor system is mechanically synchronised and if the gear train skips a tooth somewhere, the blades run into each other, not good.
Same report indicated that the troops found themselves surrounded and in a firefight when they went down. Shades of Somalia. I think the enemy had the same trainers in both cases. 'Course this time the AC-130s and BUFFs are on station, as well as fighers and Apache gunships.
True about the RPG and the flare dispenser. Any aircraft is vulnerable if hit in the right place particularly an RPG. If the rotors become unsynchronised that is a huge problem, one which cannot be recovered from. The gearbox won't skip a tooth somewhere, the entire gearbox would explode first.