I take it that there is a sync shaft so in the event of a single engine failure, the remaining engine can drive both props / rotors (or whatever they are called on this aircraft).
To not have an autorotation capability seems 'unwise' to say the least - can this really be true? Double engine failures are rare but they do happen. I know the crew that autorotated an RAF Chinook to an engine off landing after what was more or less a double engine failure in recent years. It's very 'brave' or foolhardy to believe it will never happen to you. Just wait and see the lawsuits and the mod programs after the first multi fatal crash.
Looking at its short, stubby wings, I bet the glide performance in aeroplane mode is appalling and terrifying. In helicopter mode, even if the blades could autorotate, the empennage would lead to some unusual handling issues and surely a massive nose down moment. Is the Osprey the worst of both worlds, helo and plank, rather than the best?