I have my music on my internal drive but I always thought that the data files were kept in the default music location irrespective of where the actual music was kept. By default, we get iTunes Library, iTunes Library.xml and iTunes Music in our iTunes folder. From memory (and I could well be wrong), it's only the iTunes Music folder that can be moved. I really could be completely wrong on this though. I quite often am. 😱
Irrespective, hopefully those two files (well, really just the actual iTunes Library file) have been backed up. 🙂