A number of the regenerating NPCs generate without equipment and don't attack.
The Scourge forces attack some of the Force of the Light troops until Light is defeated. The Scourge troops fail to disengage, looping their attack animation against no apparent target. Maybe targetting Highlord Darion Mograine, who remains a green target to the death knight throughout. The number of troops for the forces of the light and the scourge did not change past 275 and 10000 respectively.
Eventually, the Highlord is killed and the lich king cut scene is triggered.