Complex sentence: During the course of investigations afterward, it was determined that Soyuz 2 had the same parachute issues as Soyuz 1, and if it had been launched, Bykovsky, Khrunov, and Yeliseyev presumably would have been killed as well.
Split into simpler sentences: During the course of investigations regarding the accident, it was discovered that Soyuz 2 had the same errors with the parachutes as Soyuz 1. Had Soyuz 2 also been launched, Bykovsky, Khrunov and Yeliseyev would have been killed as well.