I had a similar problem at one time. I was nearly sick about the possibility of having lost all my notes.
Like many here, I use multiple back-up methods. Surely they won't all fail! At least not at the same time?
I have two 1G 2.5" bus-powered drives for TimeMachine. One is connected to my MacBook Pro when it's connected to an external monitor (that happens daily when we're in town). The other is in a safe inside a heavy zip-lock plastic bag where it would have a good chance of surviving a fire or plumbing crisis. They are switched out every few weeks, but it should probably be weekly. I back-up to TimeMachine immediately when I've made several changes. Who says we have to stick to the TimeMachine default schedule?
I regularly move critical files to my Mac mini. AirDrop is great for this, because at that point my machines are side by side.
I make text copies of my entire user notes file on a regular basis and save it as an rtf. That would mean a lot of reformatting if I ever had to do it, but that is better than a total loss.
Finally, I have one of those mini USB flash drives (Verbatim Store 'n Stay 4GB - http://www.newegg.co...61&ParentOnly=1) that lives in my laptop. I can just drag my Accordance folder, or part of it, to the drive after each session and have an up-to-date copy at all times. It's only USB 2, so the transfer can be slow. I need to see if I can find one that is USB 3.
The 320G drive that came out of my MBP when I upgraded to a 750G drive is no longer large enough to accommodate a clone. Guess I need to do something about that.
It would be better if more of these processes were automatic. That the big advantage of TimeMachine. But dragging and dropping doesn't take all that long, and it can happen while I'm doing something else.
13" MacBook Pro High Sierra Acc 12
mid-2017 3.5 GHz Intel Core i7 (2 cores)
16 GB RAM; 512 GB SSD
iPad Pro iOS 11
iPhone 8 iOS 11
Used for backup only:
Mac mini High Sierra Acc 12
late-2012 2.3GHz Intel Core i7 (4 cores)
16 GB RAM; 1.12 TB Fusion Drive