Non-PC - agree all (post 1057).
HC - rotor brake would make a difference if applied after engines were shut down and RRPM dropped, but then maybe only a bit - if the collective was just left high with no power would the rotors totally stop or windmill slowly? I would guess the latter, though I wonder when the AAIB say they were not turning on impact they mean exactly that - or could it mean just not turning fast enough to be damaged on the leading edges?
Do we know whether the engines were both actually switched off or not? I don't think so yet. Be interesting to know.