MG,
fail? how do you mean? It's French...
They have not given us a means of controlling the engines should both channels of the FADEC fail; the metering valve will freeze in the last position. You then maintain the status quo until landing when you then shut down the engine with the FADEC problem.
Originally the idea was to have beeper controls for the metering valve motor, but it was found to be too difficult to control and was binned. In the near future a modification will be added that allows the 'good' FADEC to take control of both engines should one freeze.