Kirnardaz absorbed the souls and decided he would stay. He commanded the dragon mount to fly.
"I will be along shortly Ardeadai." Kirnardaz turned into the tornado again, letting the instability run rampant, burning through soul after soul, while tendrils ripped the souls from living guards to quench the thirst, like a spinning void, sucking in every sign of life and intelligence, rendering the guards as corpses, their souls devoured by the snaking tendrils of the life devouring storm Kirnardaz had become.
Eventually, Kirnardaz had enough souls to maintain flight to his mount, and he took control, becoming a huge winged demon, three times the size of a man. Then he took flight, leaving the fight behind.