Lucas may not have believed he would be able to make a sequel at the time, but it can hardly be said that, at least on some level, he didn't have plans for one. I don't imagine there are too many intentional one-offs that have the main villain survive the conflict and just wander off with no explaination.
Personally, I'm not that fond of the acrobatic lightsaber combat either. Too much flash, not enough drama. Something in between would be nice. Maybe one part TPM, two parts RotJ, with just a dash of "I am your father."