Alexander Payne's Downsizing has had a mixed reception - including from us, but the concept itself is pretty solid. It explored the question of whether we're doing enough to combat the waste caused by our own existence, as a character muses that humanity is heading to an extinction-level reboot of the species. But in the original version of the film, this wasn't a hypothetical.
In an interview with Cinema Blend, director Alexander Payne revealed that Downsizing had a couple key scenes, including the opening, that he cut due to length. Basically, they turned the tale of Paul Safranek (Matt Damon), a man who shrinks himself so he can waste fewer resources, into a legend:
There were a few scenes, and a framing device - that all of this is being told like a myth from tiny people 5,000 years in the future. The big extinction did come, wiped everyone out, and then we pick up the story with the tiny people who have repopulated the planet coming out of the vault 5,000 years in the future. And an old storyteller is telling children around a campfire. "Years ago, the world was ruled by giants." "Ohhh!" "But the giants were always hungry, and they fished all the seas, and killed all the animals, and burned down all the forests, and made the world unbearably hot!" "Ohhh!" And then he starts to tell the story of Paul.
This follows the third act of the film, where Paul discovers a doomsday biosphere hidden underground, where miniaturized people can live on for generations after the planet has died out. According to Payne, the opening and closing scenes of the film would have confirmed that the planet did become uninhabitable, and it would have followed the generations who hid themselves away for thousands of years, listening to tales of the Great Paul Safranek. But I've got to be honest, if I had to hear stories about Matt Damon my whole life, I probably would have pulled a Fallout 3 and escaped that bunker first chance I got.