For all the twists and turns the show has taken to this season, I feel like the end stages have clearly been more about playing out the storylines in grand fashion, as opposed to wild shockers. That said, I feel like there are only 5 people who could possibly kill Cersei.
Sansa - For how she treated her and the role played in the death of Robb/Ned.
Arya - Well, she's on "the list"
Jamie - This whole romantic brother/sister story is odd and could end oddly
Tyrian - Not likely, but they have clearly hated each other since childhood.
Cersei - She almost drank poison at the Battle of Blackwater, I can see her doing that while the rest of Kings Landing burns.
No one else makes any sense. She's such a strong and evil btch of a character, you're not writing her off in some knife fight with a Sand Snake.