This part of the mission is completely not interactive. After giving the Book to the shaman, he will head to the middle of the village and let Hermaeus Mora possess him. As a result of his sacrifice, you will learn the last Word of the Bend Will Shout and the old man will die. Now you just have to defeat Miraak inside his own prison - Apocrypha - as part of the next mission: At the Summit of Apocrypha. Prepare well for it - it's the last mission of the main story!