This is exactly why I keep an unencrypted backup on a CD/DVD or spare USB key I'm not using anymore.  Unless you're worried about someone physically breaking into your house and stealing the key, this will guarantee you can't permanently lose you wallet like this.

Btw, from looking at the source code, it looks like the key is actually created from applying someHashFunction^25000.  I'm not sure you'll find any rainbow tables for that.  

If I were you, I'd write down everything you think you can remember about your encryption password, and save it so that if you need to seek help figuring out the password, we can narrow down the search space.  Especially if it was a lot of coins and a long password.