Everything is the same up until the end, but we get to see the lives of the alliance afterwards. Pieck, Reiner, Gabi, Falco, and Annie return to the mainland, but are now homeless and they and their families are destitute and facing starvation like many others. Instead of celebrating their stopping the Rumbling the other mainlanders are too focused on surviving and don't really appreciate their only saving 20% of the world. Some even blame them, which makes Reiner realize that the Rumbling was partly his fault and worsens his suicidal outlook. The Paradis side of the alliance comes to the mainland to join up for peace talks, but they fail. They crowd points out that Paradis is building up their armies, blames Eldians, and maligns them as devils.
The entire alliance returns to Paradis, as in the manga. Historia tries to have them protected from an angry populace, but Pieck winds up getting lynched. Historia imprisons those responsible, but this backfires, since the power of the titans is gone, she doesn't have the same kind of claim to the throne she had before. There is another coup, Historia is killed and force-fed to her daughter for irony's sake, who is later also killed. Most of the rest of the alliance are killed off now that Historia is gone. Annie flees Paradis and tells the mainlanders about this. She also finds that her father died of starvation while she was gone. She winds up too depressed to go on and wastes away until she dies.
Reiner, Mikasa, and Jean run away to the woods and hide, where they spend the rest of their lives. It's left open up to interpretation what happens to Reiner. Mikasa and Jean have a child, which Mikasa decides to name after Eren to honor him. Years pass, and eventually Mikasa succumbs to old age and dies she is buried next to Eren instead of Jean.
As generations pass, the rest of world recovers and Paradis is carpet-bombed. The descendant of Mikasa we see at the end of the Manga is shown staring at a tree. Suddenly, a pig appears and a pigeon swoops down on its head. She is told that they are Eren and Mikasa and they guide her to the tree telling her that worm-kun the source of the power of the titans resides there and she is free to do with as she wills. Instead of taking the power for herself, she decides to destroy it once and for all and poisons the water, killing worm-kun. The story the proceeds to blatantly rip off the Ending of Platinum End. Without the "Source of All Living Matter," all life on Earth vanishes and people disappear out of their clothes.
We then cut to Gothkasa, Armin, and Eren in a theater. Gothkasa liked the movie, but Armin disliked and called it nonsensical. Eren says he liked being able to watch it with his friends and jokingly calls Armin a nerd for getting worked up over a movie. "No refunds," he teases.
The end.
There you have it. In my version, most of Eren's friends die before the Curse of Ymir would have killed them, so everything he did was for nothing and only made things worse. It even results in ripping off another bad anime ending and results in the total destruction of life on Earth.
