You think that Cersei would allow the Mountain to kill her and Jaime’s last remaining child right in front of her, for her benefit?
Hell no. What kind of cliff hanger would that be? The Mountain vs Tommen….who’s gonna win!!?? As I said, the faith could call Tommen, but he can just refuse. Tyrion asked Jamie to be his champion, he refused.
Last time we saw the Hound he was alive. Badly wounded but alive.
The High Sparrow may be a master manipulator but I doubt he’s good enough to convince Tommen to effectively kill himself by volunteering to fight The Mountain.
I could see Cersei killing him though, if he completely turns against her.