Game Of Thrones: 8 Ways Season 6 Spoilt The Winds Of Winter (And 3 It Didn't)
2. The Mad Queen

After years spent next to the Iron Throne, being Queen (by marriage to the King), and then Queen Consort/Regent/Mother/Dowager Queen, Cersei Lannister is finally sitting on it, with a crown placed on her head, and Qyburn declaring her the new Queen of the Andals and the First Men.
This comes after she decides not to bother with her trial, and instead burns down the Sept of Baelor with wildfire, killing everyone inside it - including the High Sparrow, Kevan Lannister, and Mace, Loras, and Margaery Tyrell, while Lancel Lannister and Grand Maester Pycelle are killed in the build-up, and Tommen commits suicide afterwards.
It's a fantastic sequence, but how exactly will it play out in the books? Much like on the show, there's a good chance Cersei won't get the trial by combat she desires. Unless Martin is going to do CleganeBowl, which is extremely exciting but also doesn't necessarily fit with the story crafted so far, nor where the Hound is currently in the books (if/when Gravedigger is confirmed, anyway). Otherwise, a trial by combat is just an easy win for Clegane against some random Faith champion (I suppose they could disqualify him on grounds of him, well, being a zombie, but it's tough to see that secret getting out).
If it does go to a trial by Faith, then Cersei will need to find another way out of it, given the charges and evidence against her. And that leads to the wildfire. In the books she is well aware of its existence, having used some to burn down the Tower of the Hand, so it's plausible that will be her go to again, especially as she has Qyburn on her side. There's also the fact that she needs to defeat Margaery, which is her obsession. Margaery in the books will be undergoing her own trial, although with weaker evidence against her, while Loras is said to be gravely injured at Dragonstone.
Cersei cannot win a trial by Faith, and she might not be able to have a trial by combat, which means seeing her burn King's Landing and take the Throne is the direction she could be headed in. As for Tommen, well he needs to die, because of Maggy the Frog's prophecy (and Myrcella will be killed at some point too), although given he's much younger, it may not be suicide, but still a result (in part) of him being swayed by the Faith.
Cersei becoming the Mad Queen fits both her arc and Jaime's. Her children are her one redeeming quality, and now she's lost that, while the books more than the show have displayed her descent into madness. For Jaime, meanwhile, he's always been about redemption, and as the most likely fit for the Valonqar, this gives him more purpose to be the one who kills Cersei.