^Best answer yet, T'Girl. Thanks for directly answering the actual situation I postulated.
Now, what if said alien race's first reaction is to "eliminate the infection" that has visited their planet and instantly destroy the ship and crew? And what if there isn't time to send a warning back to Starfleet, and they send another ship to see what happened?
(Yes, I guess that's kind of similar to A Taste of Armageddon and/or Return of the Archons)