Can the newly contracted Bell V280 Valor operate on one engine?
Yes, the V-280 Valor is equipped with a driveshaft which distributes the engine power from the nacelle with the inoperative engine to the one which still does. This system allows the aircraft to continue to operate in case of a single engine failure (but obviously not both :D).
A similar approach was taken with the predecessor of the Bell V-280 Valor, the Bell Boeing V-22 Osprey. A nice aviation stackexchange question about this system can be found here.
In this source is is stated, that this system also contributed to the design decision of the V-280 to have fixed nacelles and tilting rotors:
The straight wing also greatly simplified the mechanisms needed to connect the rotors with a driveshaft to keep them coordinated and, in case of an engine failure, both rotating. That, in turn, eliminated the need for a mid-wing gearbox, a device that adds 292 lb (132 kg) to the Osprey’s weight and expense to its price.
Which again emphasizes, that the driveshaft between the two nacelles distributes engine power in case of an engine failure.