They all drop dead within seconds and the scientists behind the plan realize: "oh shit! We forgot about [X]". That would actually be pretty morbidly funny.
Every space organization on Earth aims to become as competent and experienced as the two which have the most of all: NASA, and Roscosmos (the successor of the OKB). Both of them have already had such experiences, and to both of them there was not a drop of humor in the instances. NASA's first great disaster was [as I mentoned], Apollo 1. The fatal fault was the slap-dash initial design of the Apollo capsule, combined with the pure oxygen environment. In a fuelless "plugs-out" comunication test, a fire occured inside the capsule. All three astronauts burned to death in less than 20 seconds, and there was nothing anyone could do except the people at mission control, 400 miles away, listen to them screaming in agony into their microphones. Russia's were Soyuz 1 and 11, both caused by mechanical problems which killed the crews (totaling 4). While all of their deaths were fast, the death of Vladimir Komarov (Soyuz 1) would've been the only one which was painless; he fell to his death due to the capsule's parachute failing, after completion of his mission.
Contingencies and redundancies are counted for down to the individual movements of pens and paper for astronauts, because, as the saying goes among rocketry professionals, "There's no problem so bad that you can't make it worse".
Edited by Blue, 30 January 2014 - 02:01 PM.