This is the reason most keyboards, and most electronic gear for that matter, allow you to backup your work to external media.
What you should have done was back up your work to a thumb drive using the backup feature of the Utilities Menu every time you did some significant work.
Shoulda, coulda, woulda, but none of this helps you now. Basically, as far as recovery goes, you are indeed SOL. Without a working backup file to restore from, now I'm afraid your only option is to start over again from scratch.
Gary