Complex sentence: He has all but lost hope for his life when, shortly before his final confrontation with the Bane, Ripred takes him aside and reveals that he has never believed Sandwich's prophecies, and thus has never been convinced that Gregor will die.
Split into simpler sentences: He has all but lost hope for his own life when Ripred takes him aside shortly before his final confrontation with the Bane. The rat reveals that he has never believed Sandwich's prophecies, and thus has never been convinced Gregor will die.