Complex sentence: K-2SO sacrifices himself so Jyn and Cassian can retrieve the data, but they are ambushed by Krennic, who has traveled to Scarif, and seemingly kills Cassian.
Split into simpler sentences: K-2SO sacrifices himself so Jyn and Cassian can retrieve the data. Despite this, Jyn and Cassian are ambushed by Krennic, who has traveled to Scarif, and seemingly kills Cassian.