If Ben had survived ANH, there would have been two, three or four years between ANH and ESB in which Ben could have trained Luke. My guess is that we would have seen a very different ESB. Maybe 2 or 3 sequences like the MF training in ANH and one or two more expo drops about The Force. Faster and more intense.

The developement of the Yoda character and puppet required an entirely different aproach. All those long set-ups and mystical, magical and relatively slow sequences didn't seem consistent with GL's method at the time (Enter: Kersh).