I filed a notice of loss, plastered the lamp posts around all the stops on the train line with "have you seen me?" leaflets and went to the lost-and-found office. So far there is no sign of the case, but I haven't lost hope just yet.
The only good thing is that my already painted unit of Plaguebearers as well as the Corpse wasn't in the case as I left them at the local GW Store to participate in the Rogue Daemon painting contest. But everything else of my Daemon army, including the codex, rule book, the Portal Glyph, the 2nd edition metal Bloodletters... everything is gone.