You killed Kas, you know you did. You even disintegrated his body to be sure. But then you think about the satchel that he threw into the glowing portal. It must have been his lich's phylactery. While his body may have been destroyed, that phylactery will allow him to return, and he'll stop at nothing to destroy you all. The only way to stop him is to follow through the portal. Leaving a message for your friends, you hold your breath, and jump...