It should be possible to get a replacement brooch using the procedure in the
Lost Items topic, but since the quest log did not update when you talked to the jeweler, that may not be enough to complete the quest.
I would have to load one of my previous saves at that point to get the inventory files for the brooch, which I couldn't do until next week.
Check your messages (click 'My Stuff' in the top menu bar, then 'My Messages').
