I don't remember Ketheric or Balthazaar's corpses having anything to say. I haven't tried Isobel or Aylin's corpses though. There's also a book in the Grymforge that says Ketheric was telling his followers he was as important as Shar in there church, it's possible he had already abandonded her prior to his defeat. Balthazaar could be a follower of Myrkul who worked for a Sharran. I'm tempted to dig up my old saves from the Grymforge and chapter two just to get to the bottom of this.
Has anyone who took the Absolute path found anything that might shed light on the situation? I'm pretty sure there's a route where Isobel is captured by Ketheric, that seems like it would have some good insights.