Have they never considered a ducted fan design instead of rotors? At altitude, at least, troops could bail out in an emergency, without getting chopped to bits by the rotors.
Already, any rotor-failure looks like it’s going to instantly cut the fuselage in half.
Only Recon and SOCOM assigned Marines are parachute qualified, so there is no bailing out for us. Parachute qualification is more common in the Army but that raises the inevitable requirement for parachutes and those are not part of standard crew or passenger on-board equipment in either service.
Actually the MV-22 and, I assume, the VX-280 are pretty crashworthy. Rotor blades have sequenced explosive bolts so they detach outward from the fuselage. The composite fuselage is pretty tough and doesn’t have an engine/transmission/rotor assembly mounted above it any longer to crush the passenger compartment on impact. And the wings are designed to breakaway.
However, the scenario you postulate, shedding a blade into the fuselage is very bad. Impact may or may not sever the fuselage completely. It might sever/damage flight controls or create so much induced vibration that the aircraft is uncontrollable. Shedding the other blades from thee damaged rotor might be a way of eliminating the vibration if you are in horizontal fight but you’ll never be able to hover even if you can stay aloft on one rotor. Eventually, you would have to shed the good rotor’s blades in order to “glide” in (and you are not gliding far on those wings). Either way, you are eventually crashing/landing really hard.
Crashing is never desirable and people still can and will end up dead but, for most scenarios, your chances of surviving a crash in tiltrotors are better than in the helicopters they replaced/are replacing.
Ducted-fan lifters have some really ugly problems. Per the wikipedia article:
Less efficient than a propeller at cruise (at lower thrust level).
Good efficiency requires very small clearances between the blade tips and the duct.
Requires high RPM and minimal vibration.
Complex duct design, and weight increase even if constructed from advanced composites.
At high angle of attack, parts of the duct will stall and produce aerodynamic drag.
The last two are the biggest problems. Weight and the fact that the ducted thruster partially stalls if the airflow over it is at a great enough angle to the intake of the duct. It’s part of why the Moller SkyCar has never progressed past a tethered hover.