He never says he's dying, he mentions being taken by the darkness. That doesn't mean he's dead. If he was dead, he would have left a corpse. Did you loot Revan's body? Or a chest? Did you see him fall to the ground and watch him breathe his last breath? I don't think so. The devs have said that they left it open for your own interpretation so that they might bring him back later if they decide he fits in with the story.