Grenville
I think what we are fishing for is that in most (all?) serviceable and reasonably modern multi-engine helicopters, there is nothing you can do with the controls that will significantly droop the Nr unless the engines are set so as to permit Nr droop.
In the Sea King, the highest matched torque I ever saw in flight in the real aircraft (we did appalling things to the sim) was 135%, which is 12% over the gearbox transient limit. The Nr and both engines were perfectly happy (it was dark, in the mountains, going down rather fast, before NVG and I was the co-pilot staring rather hard at the engine gauges - the captain was a bit busy Aviating). I find it difficult to believe that a 35-yr-younger design wouldn't do better. And personal experience tells me that the rotor brake has no chance against the engines. So I'm assuming that, regardless of how the controls were handled, if the transmission was serviceable and the engines were running at governed Nf/Nr, the rotor would have been turning. Ergo, as the rotors were stopped at impact the engines must have been below governed Nf/Nr, and quite likely stopped, whether because wound back, shut down or for some other reason.