KG wouldn't have made a difference. Without Posey, the Celtics didn't have a chance against the Lakers. Lakers added both Bynum and Ariza this year.
Ginobili wouldn't have made the difference either because he's a backcourt guy. Bonner/KT/Fabricio would have gotten eaten up by either Pau or Odom. If the Spurs want to get back into contention, they gotta do something about the Center/PF spot (whichever one Duncan doesn't play).
Yao/TMac/Deke, that would have made a difference
Jameer at 100% would also have changed the complexion of the series