Jon Snow decides enough is enough and that breaking his oath is the right thing to do, thus growing as a character by learning that morality is more than just your Word.
He takes a stand against Danarys Targarean, but not wanting any more blood to be spilled, convinces her to put the fate of the Iron Throne and the Seven Kingdoms into a trial by combat: Jon Snow vs Grey Worm.
Jon defeats Grey Worm in combat, but Dany does not accept the victory and, in a rage, commands Drogon to kill Jon. "Dracarys".
However, Jon also has control over the dragons as he is a Targaryean, and sticking his hand out, Drogon backs off.
As Dany goes to order the Unsullied to slaughter Jon and the rest of the Northerners, she's stabbed in the back with a dagger. She turns around to see that her attacker is none other that Tyrion Lannister, who is hurt that someone he put so much faith in could let him down so horrifically but did what he had to do to prevent her from killing more innocents. With her last words, she tells him angrily that she can see why he defended his brother so much as they both stab those they swear loyalty to in the back.
Jon takes the Iron Throne, with Tyrion has Hand of the King and Davos Seaworth as one of his advisors. He sends Drogon to live in solitude in either the Northern or Southern continents (my dad and I found an interactive map of Ice and Fire, and Westeros and Essos are only two of four major continents) as there is no place for a dragon in Westeros. He commands the Unsullied and the City Watch in King's Landing, and the Seven Kingdoms unite around him. The world knows his true lineage as both Stark and Targaryean, and his story will forever be a Song of Ice and Fire.
And then it ends with fans taking to the Internet to scream about how the writers deliberately ruined the show forever.