Well that stinks. I'm sorry
Well, this time around you can set it up so that you always have a copy to go back to. If you want to do it simply you can, every day or every few days, copy your files to a different directory so you can always go back to older ones if need be. Or you can use a version control system. I use git. I'm not sure if you've ever heard of it so I'll explain about it a little, just in case. Using git you can commit your changes in a piece-meal fashion. If, at any time, you want to go to an older version you can easily. You can also make copies of your projects super easy that will also have all your history of changes. It even makes it easy to put your stuff up for people to collaborate on a site called github.com, if your so inclined. I've got an a few animations there, myself: https://github.com/lungching
If you're interested in learning more I just came across this git tutorial: http://gitimmersion.com/index.html
I hope this helps!