Like any aircraft that loses all power, a safe landing will depend on the several factors: aircrew performance, weather and flight envelope. Will the aircrew be trained to attempt a landing if in the unlikely event that both engines are lost in the same flight hour; the probability of which is 1x10(-10)? Yes.
Now some questions for you, oh nattering nabob of negativity. Can a CH-53E land safely if it loses all three engines and its tail rotor? Can a CH-53D land safely if it loses both engines and its tail rotor? Can a CH-46E land safely if it loses both engines and its tail rotor? Can a UH-1N land safely if it loses both engines and its tail rotor? Can a AH-1W land safely if it loses both engines and its tail rotor? Can a VH-3 land safely if it loses both engines and a tail rotor? Can a VH-60 land safely if it loses both engines and its tail rotor? What are the MTBF figures for powerplant failures in the above helicopters? What is the MTBF figure for the powerplant in the Osprey?
/2/ If due to mechanical failure or battle damage, the rotors cannot convert from forward to overhead, can it land safely?
Once again you ask the wrong question. The question you should have asked is can the Osprey attempt to land if the engine nacelles cannot be tilted? The answer to that question is yes. The design of the proprotors, which has been confirmed in testing, is such that they will broomstraw when striking a solid object. The proprotors do not shatter. Incidentally, in the ~8,000 hours of flight testing there has never been a single failure of the engine nacelle tilt mechanism.
/3/ How can it fire weapons forward for protection, now that the nose gun has been removed from consideration as too heavy?
The nose gun has not been removed. The contract for the GDAS GAU 19/A was awarded in the first quarter of 2001. All production MV-22s and CV-22s will be equipped with the gatling gun.