I don't know why this hit me last night, maybe it was watching Cersei being backed into a corner more and more, but I think that Jamie is going to kill her before the end. I think that Tommen will die, possibly poisoned by Margery, and Cersei will lose her **** and try to burn the whole city to the ground. Jamie will kill her to stop her (Mad King part 2), and then kill himself.
Of course, this could all be proven wrong if Brienne kills him in the next few weeks.