It took a while for the Barrow to be fully dug out, and Ararvyne knew that something deep within it was egging Ralis Sedarys on. So it came to no surprise when he arrived and found dead bodies around the encampment, or when he read the journal entries. After retrieving the rest of Ahzidal's relics and dealing with Ahzidal himself, all that was left was Ralis. Going against a Dragonborn, his mercenary, and a Seeker, he'd knew his life was at an end.
But Ararvyne offered to spare him in exchange for his eternal servitude. Ralis' soul was now under his command. In the end, Teldryn Sero was released, as Ararvyne could feel that his need for an extra sword was coming to an end.