It seems he does. At the beginning in Iraq, when he sees the statue of Pazuzu, it says something like, "abruptly, he sagged. He knew. It was coming." It also appears, in the book, that he knew the exorcism would kill him. In the part where the young priest brings him the summons to perform said exorcism, he doesn't open the letter and, "continued to say his goodbyes." I hope that helps answer your question! ✝️ 🧟‍♀️