Spoilers ahead for Game of Thrones Season 8. Daenerys might have once been the Breaker of Chains, but this Targaryen didn't go to King's Landing in "The Bells" to liberate it — she came to destroy it. And with this dramatic shift in character, Daenerys may kill Tyrion on Game of Thrones in the series finale. Before she decided to slaughter thousands of innocent people in the streets of King's Landing, Daenerys had executed Varys for conspiring to overthrow her — just as she had promised she would do back in Season 7. She told Tyrion he'd be the next advisor to go if he ever failed her again. So Daenerys could kill her Hand before Game of Thrones is over if someone else doesn't get to her first.
After eight seasons, Daenerys can finally say that she rules Westeros. But the show betrayed her character by having her rapidly descend into ruthlessness, killing the citizens of King's Landing after Cersei's army had surrendered. She chose to obtain her power by fear after the deaths of Viserion, Jorah, Rhaegal, and Missandei; the attempted treason by Varys; and the revelation that Jon has a better claim to the throne than her (and the fact that he won't reciprocate intimacy anymore since, you know, she's his aunt).
So even though Tyrion has been devotedly serving her since Season 5, the Daenerys in these last couple of Game of Thrones episodes is not the Daenerys fans thought they knew. And since Tyrion freed his brother Jaime, Daenerys will certainly feel (and unfortunately be) justified in executing one of her last allies.
At this point, it doesn't really matter that Tyrion freed Jaime and sent him into King's Landing to try and save Cersei because both of his siblings died in the rubble of the Red Keep. But Tyrion schemed with Ser Davos Seaworth to smuggle Cersei out of King's Landing — choosing his family over his queen, just as she has accused him of doing before. Daenerys explicitly told him before the attack on King's Landing, "The next you fail me will be the last time you fail me." And when he released Jaime, the Kingslayer warned his little brother, "Your queen will execute you for this."
Tyrion seemed to understand that he might die for his attempt to save his siblings and the people of King's Landing. But he also had a moment that upon reflection is too painfully optimistic based on the rest of Daenerys' actions in "The Bells." He told Jaime, "If Daenerys can make it to the throne without wading through a river of blood, maybe she'll show mercy to the person who made that possible." But, uh, yeah — that's not gonna happen now considering that Daenerys actively and unnecessarily chose to create a river of blood to conquer King's Landing.
Daenerys wanting to kill Tyrion seems inevitable. But Tyrion's allegiance is also going to have dramatically shifted since he has seen how right Varys was. In the preview for the final episode, Tyrion isn't by Daenerys' side when she goes out to give a friendly greeting to her new war-torn kingdom. So as he assesses the damage she has done, maybe Tyrion will flee the capital. Or maybe he will plot with the other people who have been misled by Daenerys — like Jon Snow, Davos, Sansa (who, to her credit, saw this coming), and Arya — to stop this "Mad Queen." Because while Tyrion wasn't comfortable with planning to overthrow her with Varys, Daenerys proved in the end to be a cruel and corrupt leader.
Game of Thrones didn't do enough to justify Daenerys' actions. But kind of like Tyrion trying to save Jaime and Cersei, it doesn't even matter anymore since she officially broke bad. So the final episode will have to navigate a world in which Daenerys is a ruthless, blood-thirsty tyrant more obsessed with her destiny than being a decent leader. And with that comes the very real prospect that she will kill Tyrion, who no longer will be able to serve her as the Hand of the Queen in good conscience. But maybe Tyrion's cleverness will finally reemerge or the information Bran told him at Winterfell will lead him to sacrifice himself in order to defeat this Targaryen ruler. Because even if Daenerys isn't the one to execute him, Tyrion Lannister seems ready to die for the sake of the realm before Game of Thrones is through.