So, just like the title says. When you beat an enemy party, all the guys who routed are still there on the map, but when you lose, the survivors just vanish. There ought to be a chance (could be based off Roguery with a perk to increase the odds) of escaping scot-free after a loss, just like npc lords can escape, and if any of your guys routed and got away, you should be able to join up with them again.