Mad Max Fury Road. They defeat the tyrant, and get the control of the water valves. Then they open the valves and seemingly keep them open. One problem, how long is the water reservoir gonna last now?
Logan’s Run. The city dwellers are freed from the computer’s iron-fisted rule, and Carrousel. But their city is in ruins, and thinks to the computer providing everything. They don’t know how to live without it. The city dwellers are going to start dying off real fast.
I always interpreted Snowpiercer (the movie) as being somewhat ambiguous about whether there were other people. We only have the word of people we already know are authoritarians that lie to keep order.
And the presence of a large carnivore at the end implies the food chain is healthy all the way down.