Honestly, I wouldn't recommend anyone to buy Office for Mac.
Especially with large files such as dissertations. I would never do critical work with Office for Mac, as I expect it to crash occasionally.
This is not a subjective statement-it's what I've experienced with all versions on several machines of colleagues and friends. If you've already examined the autorecovery files in ~/Documents/Microsoft User Data/Office 2011 AutoRecovery and there's nothing, you're out of luck.
