Good list, but I think Harkless at 3 might be a little premature at this point. If we make the NCAA tourney this year (not holding my breath), his departure won't be viewed as being that damaging at all. In fact, it will be viewed as a good thing for future recruits
If Cook came back, he would have played with Hatten. While on paper that seems great, I am not sure they would have meshed as Hatten played better when he had the ball.
If Barkley came back he would have theoretically played with Cook. While that would have been interesting, I am not sure how much of a win loss difference that would have made for that team.
If Harkless came back this year I think sweet 16 would have been in play.