As far as the question of "Who kills Cersei?" goes: Remember her fortune said she would be queen for a time until a younger, more beautiful queen cast her down and took all she held dear. Then the valonqar would kill her. Everyone assumes valongar means younger brother, so Jaime or Tyrion makes sense. But valongar is neither gender specific, nor possessive. It simply means younger sibling. Not even YOUR younger sibling. And that opens up some other possibilities. At this point, everyone (probably safely) assumes the younger queen will be Dany. What I find amusing, is that while Sansa was betrothed to Joffrey, Cersei wondered if it would be her, and then dismissed it since she considered Sansa dim witted and naive. It's almost a certainty that Dany takes over, if only for a time. But it would be funny if it ended up being Sansa. And regardless of who takes the throne, a younger sibling could still be Arya. Hell, it could be Jon since he's the youngest of Rhaegar's children. If I were a betting man, I'd say it's Arya... disguised as Jaime.