It should be quite simple to either discard GT's scenario outright or to leave it in the category "perhaps that's what happened". All one needs is the last part of the flightpath, the exact location of the crash, the low level winds in the area and the vertical stability of the atmosphere in the area. All this information can be relatively easily sourced. Then with a good understanding of air flow around mountains and perhaps a numerical model simulation, one can find out if such a rotor-system could possibly have been present at the time. Knowing the flightpath of the second helicopter and talking to its pilot should also shed light on this question, although such rotor-phenomena can be rather small - as every glider pilot knows who has flown in the mountains. I'm sure ATSB will do all this.