The Twilight Zone, "Two," 1961

Another heavy-handed Cold War parable from The Twilight Zone. Wikipedia already contains a fine synopsis. While it is never specified that the characters are the only remaining humans, the shadow of The Shaggy-God falls over the whole affair.

Even though billed in the voiceover as taking place "perhaps a hundred years from now, or sooner, or perhaps it's already happened two million years," Charles Bronson speaking English and Elizabeth Montgomery speaking Russian doesn't leave a lot of wiggle room. At least we are spared them being explictily identified as Adam and Eve.

Season 3, episode 66, written and directed by Montgomery Pittman.

While the similarities are suspicious, I imagine John Christopher's "Two" (1952) was probably not directly taken by Pittman for his plot. The durability of The Shaggy-God story is such that it seems to spontaneously erupt in science fiction cautionary tales. It was used in at least two other Twilight Zone episodes, after all: "Probe 7, Over And Out" and "Third From The Sun." (Although to be fair, "Third" is really more of an "ancient astronauts" riff.)