What if instead of teathers, you just had two large circles of composit, as a hub and a rim, that were stiff enough to keep all wing positions but stiffer than a flimsy string - and thus keeping formation?
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.
Added: OK, it is all generated by the centripetal force caused by the mass of the wing units. So fast spinning and lots of cable/parasitic drag to get the wings reasonably level. Seems like a lot of wing area for a small payload. How is this better than just a wing large enough to support the payload with cables to distribute the load across the wing length?
Added2: This scheme still has the problem that the downwash from each wing will affect the other wings, just like in the helicopter case.