That is a very valid point - one of my deep regrets about Divinity was that the war didn't get visualized like we had planned it. The usual reasons applied. I also thought btw that the way they did it in Diablo was quite good.
But it means the monsters should've respawned, or else NPCs would've just killed each other before the player had the chance to interact with them!
Does BD have respawning monsters except for Battlegrounds?