From the last book as stated by Wiki... Last of Jedi Spoilers Ferus seemed to give up everything after Roan had died. Even life itself. He knew he would be executed; however, the Emperor showed up unsurprisingly and offered to halt the execution. He offered Ferus his teachings, ones that could control life and death. After catching Ferus' attention, Palpatine consented to Ferus' agreement which was secretly made to kill Darth Vader and avenge Roan's death. "I'm ready to learn." Ã¢??Ferus Olin So it could be possible. I can see it now the all powerful Olin is about to destroy the Emperor and Vader, then a voice comes out of no where. I don't think so...Olin looks and it is Obi-wan. He stops Ferus and explains his plans to him involving Luke so Ferus will not fall to the darkside. They leave the Emperor and Vader alive. Later Obi-wan is comminucating with Yoda all proud of stoping a Jedi from fallign to the Darkside. Yoda listens and replies "Screwed up again, you have" Obi-wan realizing nothing that has happened in the last 10 years makes sense..."Oh Crap"