A family member was updating photos on her Mac the other day.
Her husband "needed" to move the Mac to use it for who knows what. The external drive was plugged in and he severed the connection like the head of a French aristocrat. The iPhoto library vanished like a ghost.
iPhoto libraries for windows users are like a locked folder with hidden files inside. The iPhoto program manages everything and the files are invisible to Finder (Mac's Explorer)
She felt the most major panic but she made the right call (to me) and I quickly determined that she hadn't built a "new" iPhoto library or accessed the external drive for anything else.
The hidden files were all there but had to be recovered with Boomerang (recovery utility software) because there was no FAT entry on the drive for them.
The happy ending is that she'll have to reorganize her photos but they're all there. We'll rebuild the library after the 10 hour scan with the paid version of Boomerang (an unhappy experience buying that software!) finishes.