As the topic is "issing orders question" let me use this thread to comment something that I was not using in my games and my regular player make me notice this summer during a game. (maybe is something so obvious).
When the general fail the order your command phase is over. So it is a regular practice to start giving orders with heros and sorcerors and get the general the last one to give orders. BUT it is legal to start your command phase giving orders with your general. If you fail, your command phase is over, but if you success with your general orders, you can declare "no more orders for general" and then continue giving orders with heros and sorcerors. When all subordinates had failed or you have ended with them your command phase is over.
Sorry ogrimdoombringer for this little hijicking of your thread. In order to answer your last question, I agree with captpiett, If a unit of the brigade is pushed by arrows the distance to get isolated of the brigade (no contact with the other brigade units), then you should treat it as a signle unit not brigade in you command phase.
A brigade with fanatic troops like troll slayers o flagellants in the front (troops that are not affected by push backs) is perfect to advance against a shooty enemy.
Undeads brigades arrays in lines (NOT single units), also are not pushed back by arrows because they can not suffer of desorganization. So the inmediate unit denies the move back, and the first unit is not getting desorganizated. It is not easy to make retreat the dead.