Their system seems to have a bug that when a game disappears from sale, it temporarily disappears from previous buyers' shelves. It should reappear soon. A staff member might have to set some flag in the database to turn them back on for download.
^^^ This. I assume removing a game from the catalog involves a database rebuild, which seems to wipe the entry across much of the website for a time. Mine has vanished too, even though I just bought it right before the change; I reckon it will be back in an hour or so, and if it isn't I'll ask support.