[TOMT] [BOOK] sci-fi novel I read in a library in late 1980s

The earth surface has been rendered uninhabitable (can’t remember why) so humans have gone to live in stasis underground. Conditions improve so humans begin to wake up and make their way above ground. Then it turns out some super rich elite people never went underground in the first place but sneaked off to live in spaceships. They send some people back to scout out the situation but they die. It turns out the earth has evolved, and the spaceship people can no longer survive in the new environment. But the underground people have evolved with it, so they can come back to live. The spaceship people are presumably doomed.

Edited: now cross-posted to r/whatsthatbook . Many thanks to all for suggestions so far. Thinking hard about it, I suspect it was a short book - perhaps a novella, maybe even a short story (but I feel it filled a whole physical book rather than being part of one).