BACKUPS. ALWAYS MAKE BACKUPS. But, most backup products are clumsy and error-prone.
I have a script, and a simple US$39 product from Germany, that allows me to make 100% backups of each computer (locally on a separate partition, with as many days' worth of backup as you'd like to have; I use 5) and a 100% copy to an ancient XP system that writes them to an external drive (which I change every 10 days or so; I keep three 1TB disks in rotation; the eldest is in the trunk of my car, so if the house burns...). Last night's backup is in three places!
If you're interested, I could post more of it here. I call it "The Waterfall" method.