ATN
Firstly, not all FADEC software logic is the same from manufacturer to manufacturer and for the point of argument, let’s forget twist throttle systems and stick to a modern top end FADEC system that uses position transducers.
In normal operation, if the collective is smoothly and gently (low rate of collective pitch change CLP) pulled up then the FADEC would schedule fuel flow through the FCU accordingly whilst governing NR.
If the collective pitch change (CLP) is slowly increased still further (even to the ceiling if that were possible), then the FADEC will continue to provide regulated fuel flow until a limitation is reached, i.e. Ng / ITT / Tq, at which point the FADEC software and hardware protection systems should prevent exceedence of any of these limitations by reducing or even stopping fuel flow through the FCU metering valve.
Note that the FADEC should allow transients above these limits during normal accel/decel operation.
Forgetting OEI operation, If say the pilot having reached max Tq in an emergency kept pulling up on the collective, I believe that some FADEC systems will sense this additional demand (High rate of collective pitch change CLP) for power and override the limitations set into its logic and keep delivering.
The theory being that if you are that desperate for additional power, safe management of the engine is not an immediate priority.