What is the ultimate fate of Arthas in WLK?

After being transformed into the Lich King by Kilgardan, Nai 'ozu always wanted to get rid of the ice. He needs a free body. So he seduced a soul wandering on the edge of darkness, Prince Arthas. What does he want as a dead man in prison? This must be a rebirth, a free body, a new life. For this reason, the Lich King should not let Arthas die. After all, the Lich King secretly loves him, not because of his strength. If you only care about strength, Lao Mo seems to be stronger, because Arthas is the best material among the living. In the battle, Illidan and the king of fear both called Arthas "human", which shows that he has always been a living human body. After merging with the Lich King, it became a living body with two souls.