“The most likely being Jamie kills Cersei, as he recognizes the woman he loves is absolutely insane and evil.”
Possible. However, keep in mind what Jaime said to Edmure Tully - tied up in the tent outside Riverrun: if necessary, he (Jaime) would kill EVERYONE in order to get back to Cersei.
Of course, he may have just been using a bit of hyperbole to scare Edmure into submitting...
True, could be Tyrion that kills her, if you go by the prophecy.
But remember he said that before he came home to find out she had done the one thing that he had killed his own king to prevent... may not have been the entire city but it was a damned good show of it none the less... that and their last child also fell victim, even if unintentional to her schemes.
Jamie obviously loves her, but he does not share her complete lust for power, to date Jamie seems to have a code of morality to him, even if it is a bit more warped than most, whereas Cersei has none.. her love of her children, evil or good as they may be, seemed to be about her only grounding .. now they are all gone.. there is nothing left to ground her at all.
Time will tell.