According with FCOM 3, FADEC fail you will have no engine indications (all amber crosses) but engine runs. One must use the ECAM system pages, such as hydraulic and bleed to confirm that engine is operating. It also states that if the engine is not operating, you should set master switch off.
But it has no further gidance for "if the engine is running".
So lets suppose that you have ENG 2 FADEC A FAULT. Later inflight fadec B fails also. So you end up with ENG 2 FADEC FAIL. You have all amber crosses and you know the engine will not quit just because you lost FADEC.
The question is: Is the engine responsive to Throttle lever movement?
Is there any relationship between TLA and the engine HMU? If not possible, that would mean cutting the engine for descent.
Cheers