Great question! Technologies that fail is really inevitable. Take the autopilot Tesla that has gotten into fatal accidents for example. 

There will have to be a lot of testing with something like a hover backpack and Lunavity should integrate a fail-safe system that will gently lower users of the backpack. I guess only time will tell what the students at the University of Tokyo decide to introduce to their hover backpack! I will be sure to keep you all posted if the techchat team hears of anything!