Let's imagine that Lost had to end after one of its earlier seasons. The writers don't compress the full story into fewer seasons, which would probably have helped the show. Instead, they just cut it off earlier, changing only the end of the finale, if anything.
How would it go?
The show could have ended quite easily after the first season. Few unresolved story arcs would remain because season one didn't have story arcs. It had character arcs, and if you believe the finale flashbacks, all had finished. Characters had crashed, had bonded, and they'd just launched a raft that would presumably find rescue, once we cut out Walt's kidnapping.
And the Others? They don't exist. Charlie says so when he retrieves Aaron: "There never were any Others! It was you!" That made no sense in the actual show, where Ethan, an Other, kidnapped Charlie. But it makes perfect sense in our abbreviated version. Ethan and Danielle were the only people on the island. Both wanted children. Ethan was Robert. Or, to stretch ages a little, Ethan was Alex.
We shouldn't see the smoke monster. It will remain an unseen monster, which makes some sense, unlike a cloud of black smoke, which you can't introduce at the last moment without explaining. We won't understand a few random things, like whispers and Polar Bears, but no harm. And the Hatch? The last shot will be Jack and Locke looking down it. A final crazy mystery which we'll never answer.
I think this would be the hardest season to end on. It did a great job of wrapping up its own stories - the Swan, the tailies, Walt, Henry Gale. It did nothing at all to further the show's story. You know, people stranded on an island? Other than Bernard's S.O.S. sign, no one did ANYTHING to try to escape this island this season. Nor did they do anything notable about living on a deserted island.
Could the survivors getting hooded remain the final shot? A purposely unresolved mystery like staring down the hatch? No. No, it can't. And we have to do something about the survivors.
I suppose the only way to solve this in the show's last moments is to reveal what we knew all along: the survivors all died in the original crash. The Swan? It wasn't just an electromagnetism station. It controlled the source of all life, death and rebirth. By blowing the dam, Desmond allows all those dead souls on the island to move on.
Nothing needs to change to make this ending work. It's perfect.
The survivors are about to get off the island. They've found rescue at last. And we have a flash forward of what happens afterward - everything falls apart. We don't need anything else.
To really make it perfect, we can replace Naomi with Penny. And she's wearing a knife-proof vest.
Another finale where we need to change almost nothing. The show ends with the main characters getting off the island, and we even see what all their lives end up like. We might have to tweak the flash forwards a little to make them epilogues instead of cliffhangers.
Sun and her dad's scene is fine. That's her future. Cut out the next scene with Widmore. To resolve the Widmore dispute, instead slip in Ben's scene with Penny and Des, exactly like it is in season 5. Get rid of Kate's Claire dream. Sayid still breaks Hurley out of the asylum, but this time, he convinces him he's not crazy. No more Jeremy Bentham. The last we see of Locke, he has taken control of the Others before the Island vanishes forever. We'll never know what happens to the island or to the survivors who didn't escape.
And Jack? Still depressed. We established that at the end of the previous season. He doesn't meet Ben and talk about returning to the island. I suppose he has to kill himself. Jack's eye closes. He is gone. LOST.
Could we end the show with the bomb going off? The ultimate "no ending" ending?
Almost. Except for what's going on the present. We can't leave a question mark on that.
So let's add one more scene to the present. Just enough to let us know Locke is the smoke monster. And there, that answers the biggest mystery. What is the smoke monster? It's a man. A man who's tried to kill Jacob for centuries. Any further info would only ruin things.
Jacob's dead. Evil has won. The world is about to end (somehow). "Meanwhile," in the past, Juliet hits the bomb.
And the show ends with the closing scene from "LA X, Part 1". All the characters are back in Oceanic 815. They land safely. None of them know each other. Nothing in the series happened. A supremely tragic ending.