That's why you never store a backup plugged into your computer.
I always say, keep MULTIPLE independent backups stored away from computer. I use old hard drives, slowly cycling through them, bringing each closer to up to date If used only for cold storage, they last forever.
You do know of course, that if you have only one backup, and your main drive goes down, you don't have any *backup* anymore. Think about it. That's what happened to you dragon.
ie... one backup is no backup, unless you are very lucky. Like me last year. I got a bit sloppy and made only one backup of my super map. My main drive went down and I had forgotten I made the backup. Went for months thinking I lost it. I found it. I got lucky, this time. I immediately made extra backups on top of backups when I stumbled across my map I thought I lost.