Yep, been there, done that, got the t-shirt (Apollonia).

There may be a temporary window of opportunity just after the enemy general dies. At least in MTW, the death causes a sudden sharp drop in morale, but then it recovers. Ideally, if you can synchronise your cavalry charges to the rear with the death of the general, you may break the enemy. But don't count on it.

Did you notice any small units of those 2HP hypaspists? Those blighters are a nightmare to fight. Think bastarnae equipped like principes and running on amphetamines. It looked like Mount made scarcely a dent in the few facing him. If do you face them, a good, well-ordered cavalry charge to the rear is your best bet[1]... so long as they are the sword-bearing, not spear-armed, type.

[1]Actually, that's probably the best bet to fight almost anything, but with hypaspists, the point is that other counters just don't seem to work.