It got knocked out of Bradford’s hands. I would guess that it and the other artifacts were either secured at the Library of Alexandria or else moved to another secure location or locations. Ludwig, Beakley, and Scrooge probably worked something out with S.H.U.S.H. to accomplish this, along with getting the various F.O.W.L. captives home and presumably trying to round up what members of F.O.W.L. they could.