Well, even tough I dislike the way Lucas treated Prowse during the filming of the original trilogy (not telling him they wouldn't be using his voice), it was probably for the best. Prowse just didn't have the kind of voice to play an evil dark lord. Most people working on the original film didn't feel the Vader had really come alive until Jones started being his voice.
So, I thnk Star Wars would be much less popular, but I think it still has a chance to be sucsessful, given the special effects, and the decent jobs from the other actors.