I'm not really tech savy, but this is something everyone should know about IMO. This may work.
Try using system restore on your computer and going back a bit before you downloaded the pets demo or any patches. I've done this many times with patches and it saved my game each time. Now it doesn't work for everyone, but it doesn't hurt to try. You can reverse it if needed, but I recommend not going back to much anyways. Pick a recent date (before the demo or patch) to restore it to and it should work. Everything should be intact, so try it.
Note: You may lose recent downloads and anything you downloaded after the date chosen, but like I said if the date too way back don't try it. I thought I should post this since so many people are have lost their games. :(
Windows 7 and Vista directions: http://www.howtogeek.com/howto/windows-vista/using-windows-vista-system-restore/
Log on to Windows as an Administrator.
Click Start, point to All Programs - Accessories - System Tools - System Restore.
On the Welcome to System Restore page, click Restore my computer to an earlier time, and click Next.
Or type or paste the following command in the Start - Run box then press Enter.
Not sure about Mac, but try google. Where I found the links above.
P.S. Also get in the habit of creating save points with system restore. I make one before every patch. ^_^