Very sad. Always makes me nervous just thinking what-if a V-22 rotor was compromised - no way back from that. RIP to all.
Although the Chinook would presumably have similar fatal controllability problems if they lost a rotor or drive to a rotor ? Presumably the Osprey has cross-over driveshafts to keep both rotors turning if an engine fails? (Would not have helped here of course, as it sounds as if a rotor gearbox broke up).