Maybe the
Save Game Editor could help? I didn't see the Fire Rune listed when I skimmed through the list, though. I don't know if you could transfer the staff from an old save and use the elemental forge again with a main character.
Please 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.