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.
Snowpiercer: Sure, there’s some evidence the world is warming, but at current there are two people, a bear, and no real shelter other than a rapidly cooling train. Just how long do they expect to survive?
The Graduate: Ends with the famous fading smile. Sure, you ran off together… now what?
Morbius: The central conflict of the movie is that the vampires who drink real blood go feral but are more powerful, and those who drink artificial blood are weaker but in control. Morbius is under time pressure because the artificial blood is becoming less and less effective, so he’ll eventually have to drink the red blood or die. He got a temporary victory killing Matt Smith, but due to the incompetence of the studio the actual real conflict of the movie is never actually resolved.
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.