Lancel Lannister will be the next person to sit the Iron Throne.
/u/faegontheconquerer, you're crazy!!
Crazy like a fox.
Let's say Cercei either loses the trial by combat (which admittedly is somewhat unlikely given the Qyborg Robert Strong), or is somehow outted as using a blood magic zombie which nullifies the trial (more likely) which would not sit well with the High Septon/Sparrow who's power is growing rapidly. Cercei's children are now de-legitimized, so the last valid ruler was King Robert. Who is next in line?
Baratheon:
Robert - Dead
Renly - Dead
Stannis - worships a foreign God, I don't see the new High Sparrow annointing someone who has literally burned the faith of the 7 let me know if there are any cousins in the mix, I am unaware of any.
Typically rule is not passed through the female line, but given the lack of Baratheons it may be necessary:
Lannister: Tywin - Dead
Cercei - exposed as a fraud or loses her trial and is beheaded (speculation obviously, but this is the basic assumption of this post feel free to poke holes in it)
Jaime - Member of the kingsguard and shows no ambition for ruling besides
Tyrion - guilty of regicide, is currently on the lamb
Joffrey Waters - Dead
Tommen Waters - is recognized as a bastard
Myrcella Waters - also recognized as a bastard
Genna Lannister - Alive, but is a woman and a Frey
Tion Frey (son of Genna) - Killed by Rickard Karstark
Cleos Frey (son of Genna) - Killed by his horse after Vargo & co. attempt to catch Jaime and Brienne
Genna had two other sons killed in the war of five kings
Kevan - Killed by Varys' crossbow for being too competent
Lancel Lannister - Alive and Kickin'! Well, alive at least.