Well, just sync it with iTunes. It should save the file in the process. I had several iOS devices for the past years and I was always able to resume my games after a restore.
Oh I guess you mean after downgrading iTunes? I guess you's have better luck by doing all this in a virtual machine or on a second partition.
Really, I can use my dad's, he doesn't use his and even wants to return it to me but we keep on forgetting every time we see each other.