Well if Darth Vader is not a featured character they can't really eliminate him entirely, that would make no sense. He's supposed to be the most feared figure in the galaxy in this time period between trilogies so at the very LEAST we might see broadcast versions of him everywhere enforcing the grip of the empire. And that might work, too. Maybe that's what they had envisioned for SW:Underworld.
I can picture him offering favorable treatment from the empire in exchange for information on where Jedi are hiding... to some of the poorest in the galaxy. Would make for excellent morality stories.