Chewbacca could show up. Boba Fett's a kid and Jango's dead, but an ARC trooper might fill the void (They're clone commandos that lack the conditioning and limitations that make most of the clone troopers controllable; basically one-man armies). There's no reason the Emperor couldn't be playable, he'd just lack that title. This setting also gets us the Clone Wars version of General Grievous, which is much better than the movie version, and the Clone Wars version of Count Dooku, who can beat the Clone Wars version of Grievous without breaking a sweat.
Of course, it's just a game, so I wouldn't have any more problem with characters who shouldn't be alive at the time being playable than I do with the characters in Smash Bros.