I'm looking for a short story about an alien from a future Earth (from an age after a nuclear explosion destroys ours). IIR he was part of a group mind and was named (?) Ushtu
I suspect this is "Courier of Chaos" by Poul Anderson.
The world of the far past was a terrible one to Ushtu — but no more terrifying than Ushtu himself was to Earthlings ...
Found with a search for "Ushtu" future Earth.
You are absolutely correct! It was indeed "Courier of Chaos" by Poul Anderson. It appears to have been one of his earlier pieces (I did not discover his work until much later on--it's odd that this one stayed with me for such a long time).
I found the book it was published in and read the piece. There's more to it than what I remembered--but I did get the jist of it--an investigation as to the cause of a worldwide extinction and change in the planet that ends up preventing this event (and obliterates source of the investigators).
That said I was rather taken by the (sketchy) depiction of this future Earth with its hive-mind inhabitants. They seemed interesting and it's a shame they vanished. I wonder if the author used bits of them in later works.