TC
The Ariel has a Free Power Turbine.
In the case of an MGB Input Drive Failure, the governor will sense Nf (N2 on Allisons) being High so will command the Gas Generator (Ng / N1 / CRPM) to minimum RPM. However, as the T/R is driven from the aft portion of the shaft, and the M/R is driven from the forward portion of the shaft, there is a potential disconnect between T/R and M/R rpms. The M/R will require you to enter auto, as per any helicopter that loses drive to the MGB.
The difference, is that the Ariel will still power the T/R in this configuration. The big questions are, since the Gas Generator is at minimum fuel flow, and therefore minimum Ng (CRPM / N1) what is its residual thrust? Will it accelerate the Nf ( and therefore T/R RPM) beyond normal limits as it won't be loaded by the tail rotor at close to min pitch? Will it start to govern effectively again if the tail rotor is loaded for any reason (I suspect it will)?
Any clearer?
JJ