Military leaders usually had only a very foggy idea of what was going on in a battle thanks to all the dust being kicked up and the simple limitations of human senses in dealing with vast distances and immense numbers of people. Battlefield communications were something pretty deplorable for most of history, anyway.
After the battle plans were made and troops fromed up there was generally very little that could be done to change anything anymore; adapting to changing situations was normlly up to individual division commanders and similar front-rank officers.
In Greek hoplite warfare it was perfectly common for entire flanks to collapse without the center or other flanks noticing anything - and for the victorius side to try to chase the routers for quite a while before realizing they could also turn around and go see how their mates fared. A hoplite line hit in the flank was pretty much as good as routed, although in the rare cases where both flanks were turned and the center enveloped there would normally be a desperate battle to the death with high casualty figures uncharacteristic of hoplite warfare.