@Bluedudu @HayashidaYuki
There's absolutely no reason to spare the general AFTER he's called the retreat.
Let his people sound the horn to retreat. The order goes out. An orderly retreat begins.
Then you slaughter the enemy Headquarters. Then parade their corpses high and slaughter their ranks as they fall back.
Fear grips the enemy. They couldn't defeat such a small town, they have unknown weapons of death and fire. Their very leaders have been slaughtered after calling to run for their lives. The soldiers know fear, etched into their bones.
The retreat turns into a rout. Every man abandons their weapons to run faster, throwing away helmets, trampling their comrades that fall with steel shod boots - anything to escape.
The cavalry chases them down and slaughters over half, sending the remainder back with broken spirits, maimed, disgraced, turning to a life of banditry and thuggery in human lands.
The BEST way to kill the enemy is when they are retreating (unless they're leading you into a trap, where they clearly are not). Most medieval armies were not destroyed on the field of battle, but in the subsequent routs after one side loses, and starts to run away. You'll learn this in any history book or Total War game.