I tried partition-recovery to fix this exact same issue with no luck.
Then I found Acronis Disk Director. The Demo found the missing drive, said it was deleted, but when I used recovery it found it and showed me how much space would be left once I finalized, but since it was the demo I couldn't.
I ended up forking out the $50 for it and within a matter of a few minutes I had all the contents of tha 500GB external Lacie drive back, woot!
backing up some important stuff from that drive to another right now.