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[GoT]Oberyn Martell kills the mountain and Tyrion is absolved, what changes?

Obery doesn't play around and just goes for the kill, wins the duel and Tyrion "wins" the trial, how does that change the rest of the series?
gpt
Things become very tense in King's Landing. While legally, Tyrion would be innocent, very powerful people would still want him dead. He either returns to Casterly Rock or Oberyn offers to house him in Dorne.

Cersei refuses to accept the verdict and likely tries to hire assassins to kill Tyrion, but is reigned in by Tywin (you can't have family members killing each other). Eventually Cersei has an "accident" and tragically dies after one too many attempts on Tyrion's life.

With Tywin alive, the High Sparrow never comes to power, and is likely killed early on.

Oberyn uses his position on the Small Council to become closer to Tommen and Tywin and works against the Baratheon monarchy. Tywin tragically becomes ill and passes. With no other obvious choices, Oberyn is elevated to Hand of the King. Trystane and Myrcella wed shortly after this.

By this point Olenna and Margaery figure out what Oberyn is trying to do, but with no real evidence against him they are powerless to directly confront him. 

Jaime never goes to Dorne. He refuses to leave Tommen's side after the recent deaths of Cersei and Tywin. 

In Meereen, the death of Barristan Selmy and exile of Jorah Mormont hit Daenerys especially hard with no Tyrion arriving to council her. She is murdered by the Sons of the Harpy and Slaver's Bay devolves into chaos. Rhaegal and Viserion are either left to starve or killed. Drogon wanders Essos.

Oberyn and Doran, under the guise of Dorne's equal inheritance laws, make a play to place Trystane and Myrcella on the Iron Throne instead of Tommen due to her being older. The Reach and the Stormlands go to war with Dorne and the Westerlands, who have allied with the Martells under Tyrion's leadership. Tommen and Margaery are likely taken captive by Oberyn and the Tyrells are forced to submit. Tommen is allowed to remain Lord Paramount of the Stormlands with Margaery as his wife.

In the North, things largely remain the same. Stannis still dies fighting the Boltons, and Jon Snow is murdered, resurrected, and eventually retakes Winterfell, and is declared Kingindanorf and the Vale.

Arya murders the Freys. With Jaime and Bronn not arriving in the Riverlands, they are unable to successfully besiege Riverrun. The Blackfish takes control of the Riverlands when Edmure is likely killed. He likely declares for the North.

The Iron Islands are still driven off the mainland but are able to maintain independence. Euron still ascends to King, but with no "bachelorette" Queens, the Ironborn likely return to raiding the coasts of Westeros. With their armies and navies ravaged by the recent wars, the Iron Throne is unable to combat them.

After years of war, Westeros is in shambles and the ruling Martell dynasty is in control of only the Westerlands, Reach, Stormlands, Dorne, and the Crownlands. Plans are made to attempt to retake the lost territories, but with winter here, Small Council member Tyrion Lannister advises that the Realm is unable to sustain more years of war. There are light raids along the borders of the Riverlands but the Kingdom of the North, Vale, and Trident are allowed to remain independent for the time being.

Littlefinger is lost. With his entire primary power base now under the rule of a sovereign nation, and the Iron Throne being fought over by two completely different powers than when he left King's Landing, he tries to get the hell out of Dodge once Arya, Bran, Sansa, and Jon figure out what he had done in the past. He is still executed.

With the last dragon far away in Essos, the White Walkers are unable to cross the Wall. Tensions remain high within the Night's Watch and the North throughout that winter, but when it becomes clear that the Walkers are still trapped behind the Wall (with council from Bran Stark, the new Three-Eyed Raven), they ease. With all of the Free folk south of the Wall and the White Walkers unable to penetrate the Wall, the Night's Watch stops their rangings and begins solely attempting to maintain the Wall.

At the end of that winter, Westeros is able to maintain a steady peace. The South gives up on trying to reconquer the North, and Trystane and Myrcella rule well under the council of Oberyn, Doran, and Tyrion. The North thrives under the rule of Jon. The Free Folk are allowed to settle the Gift. Life is good.