Extensive testing had revealed that every aspect of Soyuz 11’s landing, save for the valve failure which occurred 723 seconds after retrofire, had been normal. This meant that had the crew been given the chance to close it manually, they could have saved their own lives, which were extinguised by the loss of cabin pressure at 935 second past retrofire. Each cosmonaut was dead 40 seconds after total loss of pressure.
Extensive testing was undertaken over the course of the next two years, during which no other manned missions were launched by the Soviet Union. Space program officials had lobbied for the inclusion of either space suits or oxygen masks in the Soyuz capsules in order to mitigate the chances of catastrophic decompression, but they had been denied by engineers seeking to save space and weight. It was determined that had even the simplest of oxygen masks been provided, the cosmonauts would have survived re-entry.
The next Soyuz capsule that went into space carried only two occupants in order to make room for space suits. Eventually, lightweight space suits were developed in order to increase the crew complement of the craft. A special environmental control system that could flood the main compartment of the capsule with oxygen was also outfitted to the Soyuz vessels.