As long as the intake valve for that cylinder wasn't open, there's a chance you can retrieve it. Since it's copper a magnet is out, but you might be able to find a gob of suitably sticky stuff to extract it, or maybe you'll get lucky and be able to grab it with needlenose or bent needlenose pliers. I'd try darn near anything short of pulling the head.

For future reference, I ball up a sheet of paper towel and stuff it in each intake runner, to prevent such occurances.

'94 extra-cab 3.0 extra slo (auto tranny) original owner. E/B o/s valve heads and no more crossover. More mods to come.