I guess we're going to assume that, for this scenario, in terms of story and character at least, everything would have ended up the same as it is now? As in, each movie would contain the exact same plot and dialogue that they ended up containing. If that's the case, then the prequel trilogy probably wouldn't have been a hit on its own two feet. As it stands, all the prequels do is flesh out the story of the original trilogy, so they're dependent on those movies to stand. By themselves, they're not nearly as interesting. Conversely, the original trilogy can stand on its own.