This happened to me also. For some freak reason, I lost ALL of my models also. Not sure what happened. I rebuilt manually from scratch. --Greg--
please tell me you are doing "File,Backup EVERY time you edit any sequences.
It only takes one second and the files are very small. You should be able to store hundreds or thousands of backups.
when you get to 100 models (Like i have), I would hate to think i need to recreate them/.