This forum seems to collect a couple of "Exmork shed its blades" stories every year.
I've seen one in person.
There are way more Bergey's than Exmork's out there, and yet we don't hear about them throwing off their blades... Mother Nature is telling us something!
Sorry for your friend; I hope he does find that missing blade. If someone else finds it, it could be a legal problem for him.