Even the .backup was corrupted? Sorry to hear that. One suggestion from me to you would be to have multiple saves that are frequent. I rotate four saves constantly so Every new save goes to the next number up to 4 which goes back to 1. After a week or two of doing that I do new saves.
Do you always X the game instead of use the quit function? I would also suggest quitting instead of X'ing but that's true for a lot of programs. While it doesn't seem different, sometimes it can make a world of difference. And I always run with the rule - everyone may say it's safe but unless you know 100% that it had nothing to do with it. why leave it to chance?