I actually did once break half of the DS spokes on our tandem when the chain overshifted and sheared off the heads of every other spoke. Since the broken spokes were evenly spaced the wheel remained reasonably true with just a shift of the wheel's dish. We moved the brake over a bit to the NDS side so it didn't rub (also adjusted the limit screw in the RDR and bent the broken spokes so they were out of the way) and continued the ride uneventfully - no need to even get out the spoke wrench.