I'm a paraglider pilot, not an aerospace engineer, so take this with a lot of salt... but:

Paragliders can have asymmetric collapses of the airfoil due to turbulence, but usually it's no big deal (other than being a little scary). Catastrophic loss of tension is avoided because there's still airflow over the rest of the glider, which remains pressurized. All the pilot needs to do is maintain safe directional control until the full wing re-pressurizes. You feel a sudden loss of pressure and then an abrupt surge of pressure, then things normalize.

My guess is that something if similar happens here, it'll happen asymmetrically, and the props might keep airflow over the other 3 wings, which are still flying. They maintain stability while the wing that went floppy drops, regains its tension, and then resumes normal flight.

Last: I'd wager that they plan on deploying these in stable air, at very high altitude.

I didn't watch the video (or read most of the page!) so it's possible I'm missing something, but the images show the wings having a propeller at each end, so I don't think a loss of cable tension would be catastrophic (at least not in the same way it would be if there was only one propeller per wing). The wing would presumably keep flying straight until the cable was tense again and it all started rotating again. Seems fairly self-correcting, with the second propeller.