For Divinity: Original Sin you could try the
Save Game Editor. I didn't see that amulet listed in a quick check, but may have just missed it.
If it is possible to sell the amulet, the NPC should still have it, so you can check the traders you usually deal with.
If that doesn't help, email supportdos@larian.com, with a description of the problem and the report.zip file generated by the
D:OS support tool (for the PC version). The report will contain system and game information, as well as your saved games. To reduce the file size, all but your latest save can be deleted from the zip.
