Those don't look like the kind of guys who "flee". Perhaps they are preparing to advance in a different direction?
They do look unhappy about the whole turn of events, and I think they were the cheif's warband, but what with Etruscan Axe Infantry and Gallic Horse and what not, they finally ran away (last of the whole army, but they did finally flee). You can see the guy with the triangular helmet and crescent things giving them some strong advice.