Assuming a rapid (and not necessarily explosive) decompression and using the emergency descent figure of 7000fpm, it would take nearly 3 mins to get below 40,000ft. Without pressure breathing and jerkin support for the chest, nobody would receive enough oxygen in the bloodstream to sustain conciousness. In other words, all on board, including the pilots, would be unconscious before reaching 40,000ft.
In the V-Force and Canberra PR9, flight above 45000ft required high pressure O2 and pressure jerkins.