For the SureFly, Hypothetically if loss of several motors caused the aircraft to be unable to maintain altitude, the aircraft would not suddenly drop like a brick, but drift down to a controlled landing.
The real emergency situation to worry about would be a total power failure. Failure of the individual electric motors will likely be extremely rare but a battery fire or controller failure could send this thing falling like a rock due to the lack of auto-rotation. It has a BRS chute but that won't do anything in the critical ~500ft band above ground level, too low to deploy normally. Additionally, I hope they've figured out how to guarantee safe chute deployment while inverted because of the tendency to tumble with no/partial power.
[0] https://www.flyingmag.com/g00/how-it-works-brs-aircraft-para...
Source? I'd think loss of two stacked rotors would lead to loss of control, tumble, and dropping like a brick (until BRS deployed), not controlled descent and landing.
That said, I would never willingly fly this thing or a Robinson, so I guess I'll never have to deal with either situation.