I had a couple of strings saved for Filename - Tag but they're missing and the dropdown window is blank. Also, my entire history of strings is also missing. They were all there yesterday. This might have happened when I restarted my machine this morning, but I don't know. All of my columns and tag panel layout are still intact.
I doubt that a restart deletes just and only the input history of one particular application esp. if that application is not even running. And even if it would be running, it would get the shutdown command from the OS.
Does your current problem have something to do with this?
Yes, backup copies are always a good idea.
You are right: save the current configuration, store it in an extra place, restore the old configuration and test that.
if the old one is too old, you can simply overwrite it with the saved configuration data.