Complex sentence: Gyepilsamun is killed by Li Kaigu's arrows, and Heuk Sudol stays to avenge him, but is killed by Zhao Renshi (Jo Insa), a Tang commander.
Split into simpler sentences: Gyepilsamun is killed by Li Kaigu's arrows, and Heuksudol stays to avenge him. He too is killed, by Zhao Renshi (Jo-Insa), a Tang commander.