this can't be solved with modding. As said before, a unit loses most of it's men after routing, because they die almost instantly then (unlike MTW were they could still do damage and break out of an encirclement). That also means lowering morale doesnt help at all, the only result is that the winner will take less casualties. Casualties for the loser will be the same.

In real life it would also be harder to chase routers because there is no godlike general floating high over the battlefield seeing were every enemy unit is on the map. Not to mension that real-life terrain has a lot more features that obstuct line of sight. And units chasing routers too far might actualy get lost and have trouble finding back their army. All this cannot be simulated wth the TW engine.