That's unfortunate. I don't know how much help it will be, but here are a few ideas.
If it has been compiled, open it from the schema browser, copy the code from there and paste it back into your file.
You can check the directory specified in your backup file preference and see if it was put there. It only backs up the last save, so maybe it's there and maybe it's not.
You can look in the directory that you normally save your packages to and sort by the date. Perhaps it was saved by a different name or something?
I hope you can find it!
Mike