I think it's about loosing a rotor, not net torque. You need to keep the roll and pitch stable in an outage.
Like that hexapod in the above link, if you lose one prop/motor/controller, you can increase power to other unit in the stack and decrease power to all the others, maintaining your stability while you descend and look for an emergency landing spot.
Only from the one pod. In all these multirotor deals, there will be other pods to make a net zero torque: not necessarily all the same pod to cancel itself out.
