I read this short story in the UK, possibly in the late 1970s.
Some guy is shown a possible future (I can't remember by who or why) and it begins with an alien craft suddenly appearing in Earth orbit....it had managed to get through the defences.
Sirens sound worldwide and mile wide deep shafts open up in major population centres, people literally hurl their kids and themselves down these shafts and tractor beams catch them, then the lids iris shut leaving loads of people trapped outside. Kaboom!
Now the guy sees the same area many years later, an idyllic landscape with lovely flowers everywhere, people ride up to verdant clifftops on giant swans or converse on white marble plazas while children play and bright butterflies swarm.
He's impressed with this scenario but then he's shown the reality, mankind's survivors are actually in permanent cryo-storage and each has a robot avatar.
The robots are really standing on desolate blasted and blackened plains with their metal jaws clacking away as they converse with each other on behalf of their human controllers
I've looked through the checklist but this is all I got (there's a minor chance it's part of a full length story, I really can't remember)