Hello @ all.
I am a retired
helicopter pilot who worked 35 years as IP in twin engine helicopters and have some EC 135 experience too.
What we trained in cruising flight, safe altitude, was:
In case of visual/audio warning of OEI or Low NR:
Lower collective immediately,aft cyclic to maintain RRPM and to reduce airspeed to Vy (60-65 KIAS).
During this manoeuver check RRPM and N2 Rpm of both engines (other indicators and WL too).
If OEI, pull collective to continue single engine,shut down proc.for failed engine.
If AEI, continue in the AR,follow autorotation procedure.
In regard to the low RRPM,I demonstrated max.range in AR with RRPM minimum (red line).If RRPM would be much lower,its true,it will not recover anymore. But I think it should be more than 5% below minimum.
For the crash in Glasgow I have no explanation at the moment.
I think we have to wait for the accident report.
Fly safe and best regards.