PBL
Let's consider fail-live.
If your FADEC sends the signal to reduce fuel flow, your engine is going to idle back.
If your FADEC sends the signal to send fuel flow to max, your engine is going to go to max thrust.
If the FADEC sends oscillating signals to put fuel flow at min, then at max, then at min, then at max,.... with a frequency of X Hertz, then ..... well, somebody who designed the system can maybe tell us what your engine is going to do. Does it depend on the value of X?
Then there are the infinitely varied other signal behaviors that can occur.
PBL
OK, now you have explained what you mean by the live and and failure modes
So in the dead mode the results and expected response by the crew are then obvious.
The fail-live mode sounds like a horror story for the crew so we really don't want that.
But there are various parameters that need to be satsfied for the FADEC to issue a command to the engine and suposedly these parameters will never line up in an acceptable range when the FADEC loses all sense of reason, thus the FADEC looks to its other channel for help and if that is also fecked up the FADEC just drops off the line and you are back to fail-dead.
I don't think that we can imagine a computer response named "Hal" in any case