How different would things be today if Rumsfeld had gone after bin Laden at Tora Bora?

Very differently. We knew we had him cornered. We knew the moral defeat of the enemy was within reach; however, bin Laden is far more valuable to US interests if he is left alive than if we took him out. Without a clear, definable enemy, we would never have been able to occupy Afghanistan long enough to build the oil pipeline to China.