ENDING 2: CERSEI WINS
Cersei Lannister, reigning Queen of Seven Kingdoms and Protector of the Realm, has proven herself over the past 7 seasons to be the cleverest player in Game of Thrones. She has long been accused of not being as cunning as her late father Tywin (Charles Dance), and she has been underestimated by all of her enemies. Nearly all of those enemies are now dead, and those that are left are marching towards the North to meet the embodiment of Death itself. We now know that Cersei lied to Daenerys and Jon about joining the Lannister army to theirs as a combined force to fight the White Walkers; her plan is to let them wipe each other out and then deal with whoever is left. A dishonorable plan, yes, but honor is for the Ned Starks of the world, and Ned Stark is dead (much of that was Cersei's doing).
Cersei has proven herself to be a true survivor and someone who has managed to climb ever higher to the seat of ultimate power in the process. By staying put in King's Landing and letting the war in the North sort itself out, she positions herself as a vulture ready to pick at the bones of the survivors. And even if the Night King wins and turns all of Westeros into Zombieland, Cersei still doesn't care - she'll just leave the continent behind to rot.
Game of Thrones could conclude with just such a scenario: Cersei saving her own skin (and that of her unborn child) and abandoning Westeros for greener pastures. As long as she - and thus House Lannister - lives, Cersei would certainly call that a victory. Still, as smartly as Cersei has played the game of thrones, she's finally made the one wrong enemy: her own twin brother Jaime. Whether Jaime will do what many fans feel is his destiny and kill his sister (or they die together) is a big question to be answered by the time season 8 ends. As Game of Thrones' greatest (living) villain, odds are Cersei will at long last get her comeuppance and won't make it out of season 8 alive.
ENDING 3: JON SNOW DIES
Jon Snow has already died once, at the end of season 5. Will he die again? It's funny to think that a man who has endured the kind of hardship Jon has, including being stabbed to death by members of his own Night's Watch, is actually one of the most blessed people in Westeros, but he is. As season 7 definitively stated, Jon Snow is really Aegon Targaryen, trueborn son of Rhaegar Targaryen and Lyanna Stark and rightful heir to the Iron Throne.
Jon and Daenerys, who is unknowingly his aunt, are poised to finally learn the truth from Bran Stark (Isaac Hempstead-Wright) and Sam Tarly (John Bradley) when they arrive in Winterfell together in season 8. This will open up a host of problems should they survive the war with the Night King. The primary one will be who gets to sit upon the Iron Throne? Daenerys has been fighting to be Queen of the Seven Kingdoms her whole life, while Jon has no designs on being the ruler of the entire country, but circumstances change, and the patriarchal society of Westeros may prefer the male Targaryen heir to the female.
Jon Snow dying a second and final time, while tragic, as Jon has been the true blue hero of the entire series, is the clearest path to the Iron Throne for Daenerys. All she would have to worry about then is deposing Cersei, which she still has the literal firepower to do (again, if she and her dragons survive against the Night King). A scenario where Jon sacrifices his own life out of love for Daenerys so that she can continue is certainly not out of character nor out of the question for Jon Snow.