Oh man. Just hearing that makes me sick to my stomach. I've lost things like that before. Luckily it was none of my writing, just some of my short films from college.
It sounds like you guys have all the info in your head anyway, if you've been toiling over the thing so much. Sounds like it's just going to take some old fashioned elbow grease and several pots of coffee. Try not to let the blues get ahold of you. Just sit down and get it back to paper, if you need it that much. Try not to dwell on how much work was put into it. After all, it's not really lost, becuase now it's all worked out and all you have to do is write it down again.
It may even come out more organized than you had it before, and offer a fresh eye so you might come up with some ideas to add or modify, or whatever.
I have my writing folder on my laptop, which is my workhorse for writing, and then I have copies on two different flash drives, and one on my computer at home. I updtae the copies every time I write something new. The only problem is that the flash drives can be kind of tricky to keep track of.
Wish you the best! Good luck!
BLG