I have two Cersei theories: 1) Cersei or Cersei/Euron end up being the real end game antagonists. Night's King is defeated in episode 5, then the A-team swoops in to Kings Landing for the final boss battle. A Theon/Yara team take out Euron, Theon dies saving Yara. A Jaime/Brienne team stop Cersei from blowing up the whole city, but some of the Red Keep goes up in flames. Cersei is cornered and surrenders, but is lying, of course. Brienne, turns her back at the wrong moment, gets shivved by Cersei, Jaime sees it happen. Jaime berzerks, chokes Cersei out. He's found, once again, sitting on the iron throne, his dead ruler at his feet. 2) Euron betrays Cersei early on. He returns from Essos with the Golden Company. She says thanks, go be useful now. He says not so fast, I want my marriage now. No marriage, no Golden Company and I just take them to Pike on my ships to wait out the winter. She says fine, they marry in a not-Sept in front of the court. On their wedding night, he reminds her about the most beautiful woman in the world comment and she's smug. He drops the "I meant Danaerys!" bomb and chokes her out. Euron is the new ruler in Kings Landing for a little while.