Might as well make a prediction, so here's my take:
Expect the most unrealistic time crunching edits to wrap this all up, but who cares at this point....
Thanks to Varys' ravens, all of Westeros knows that John is the rightful heir to the Iron Throne. He returns to the North, where everyone demands that he make his rightful claim. The Stark sisters rub it in his face that they were right, he should have listened. The North demands war to expell Dani the Usurper. John reluctantly agrees.
Dani is past the point of redemption at this point. She's become even worse than her father the Mad King. She is consumed by the fact that everyone around her has betrayed her. John rejecting her was the last straw. All she has left is her dragon, the remaining unsullied & Grey Worm...who is just as hell bent for revenge as she is. Like Aegon the Conqueror, she has just become another Targaryen who is obsessed with the conquest of Westeros, and will do it any any cost. She wants revenge on everyone now, especially John. She'll burn down Highgarden, Dorne, the Vail & all the rest on her way to Winterfell. If she can't have Westeros, no one can.
Tyrion doesn't go back to Dani. He has nothing left now that brother, sister & Varys are dead. He'll go to Winterfell & have one last rekindled love moment with Sansa. He'll discuss war options with Sir Davos. When both armies meet outside Winterfell, he will attempt another treaty to avert war, as he has nothing to lose. He will beg her to fly back to Mereen & be happy with Daario Naharis. But Dani will refuse, roast him, starting the battle.
Not sure where it goes from here... Battle ensues. Some more fan favorites will die in battle. Podrick? Gendry? John & Dani will have a moment together during the battle. Dani is so enraged that she will try to burn John, but her dragon will refuse, since he bonded with John in Season 7 & senses John has Targaryen blood. Even her damn dragon has betrayed her! He will still lack the conviction to kill her though (like Ygryte), so she will fly off. Briann of Tarth cuts off Grey Worm's head and the Northmen kill the remaining Unsullied.
But Dani still has the dragon & can kill them all. I recall Bran saying something seasons ago that the children of the forest, the white walkers, and dragons are all connected....all bound by magic & the 3-eyed raven. When it appears Dani is about to burn them all, Bran will sacrifice himself & with magic destroyed the dragon will disintegrate & die. Dani is left all alone, broken & powerless on the battlefield. Surrounded by the Starks, Arya will say something momentous, like the North remembers, as she cuts her throat. The final war is over.
John claims the Iron Throne. The Starks rule all of Westeros. Was there ever really any doubt??? Roll credits.
Another thought I had was that John gets blasted by dragonfire, but he discovers he does not burn due to his Targaryen blood. When this happens his sword Longclaw ignites in flame (aka Lightbringer from the Azor Ahai prince-that-was-promised prophecy). We are shocked to realize that it turns out John is the light & Dani is the darkness. He then kills Dani & vanquishes "the darkness" from Westeros forever. That would be bad-ass too.