bucker1973
Dont confuse Mmo with Vmo.
Both of these speeds (Mach No. and IAS) will be nominated and promulgated by your company to derive the range circles.
I would say that your aircraft is indeed quite capable of drifting down at Mmo and MCT on the live engine untill you reach the nominated diversion IAS. That may or may not be Vmo.
Whether or not the Captain elects to fly that fast is quite another matter. But if these speeds are nominated to achieve the desired range circles then the fuel to fly at those speeds must be carried.