Complex sentence: The Boss, believing that Zinyak is lying, pursues Keith into his nightmare with the help of Roddy Piper, who is ultimately unable to bring himself to kill his friend and rejoins the Saints, barely able to tell them where Kinzie has been taken to.
Split into simpler sentences: The Boss, believing that Zinyak is lying, pursues Keith into his nightmare with the help of Roddy Piper. Keith is ultimately unable to bring himself to kill his friend, Roddy, and rejoins the Saints, barely managing to tell them where Kinzie has been taken to.