We have these on our tandem, on for the back brake and two more for the gear cables (Rohloffs have two cables).
We broke a cable at the splitter in Orton, on our way to Carlisle on LEJOG. I was still able to change gear, in one direction by using the twist grip in the normal way, in the other by grabbing the loose end and giving it a tug. When we got to Penrith, Aragon's excellent bike shop fitted a new one for us.