I thought you might benefit from my experience. I had a windows 10 update refuse to install so after doing everything with DISM and sfc I decided I needed a windows reinstall. I went to windows file and scan and selected “reset this pc” and further selected the option to keep all my files. The reset deleted everything of value including MSFS and the file containing all my passwords. I finally remembered my Microsoft log in so I recovered MSFS in a new download. However, the old files were still on the drive but the links were deleted so I downloade an all new MSFS which doubled my available disk usage. In the end, I deleted many thousands of files. Good news is MSFS is running fine but now I have to update a few add ons as well as the other apps I have on the computer. I should have heeded the advice I’ve read: backup you community file and any thing else important. BACKUP, BACKUP, BACKUP.
Did you lose anything permanently, or is it just time lost?
I forgot to do this early on in my career with an excel spreadsheet I’d been working on for many hours (without saving) and due to a powercut at work lost it all and I had to do it all again (stayed at work 'till around 9pm from memory until it was done). Slightly different from your situation but a similar principle I think.
Since then, I always ‘BACKUP, BACKUP, BACKUP’.
As that bloke said though (apparently Friedrich Nietzsche following a quick google) what doesn’t kill you, makes you stronger. Bet you don’t do it again.
Hope you didn’t lose anything important 
It’s worth repeating: ‘BACKUP, BACKUP, BACKUP.
All - Worked in IT for years, BACKUP and rinse and repeat. So here is what I do, may be to many places as get confused but don’t lose much.
D:-On PC 6TB Backup Drive which is primary BU device
2nd - 8 TB WD USB Drive is the next one I backup too, when I think about it but normally a folder or file changes, I do it then. Store everything to 8TB from D, plus lots of movies too.
3rd - 4TB WD USB Drive - This one is getting long in the tooth, slow USB 2.0, so takes a while to move big folders (music is 500+GBs so it takes about 4 hours or so) Going to replace this one with either Samsung or WD 4TB SSD because faster transfer rate, and new.
4th - 1TB SSD-USB Scandisk drive, only FS stuff gets backed up to this one. Again, when I think about.
Which reminds me, need to back up some big things and so now I will do that. Thank you for the reminder.
When doing my backup, I do D all the time as matter or course, it’s my basic file save place, nothing on C but OS and X-Plane 11-12. D is my go-to file store/backup place. The 8TB is PW protected so login and then backup. In Fact, all the external ones are PW protected.
I have a similar career. First, thanks for sharing, this is really how to do data backups the right way.
Second, with that many backups I can tell you’ve seen some things. 
I had my 8TB too full, and it went south for some reason. I lost hundreds of movies but learned never to let it get fuller than 85%. So more judicious than used to be.
Years ago, PC died, lost financial stuff, and a whole lot more. Now paranoid, so maybe overkill, but almost protected.
Thanks for all the replies. I’ve enjoyed reading each. I’ve found another problem in all this: my 1TB SSD seems to have much less available space than before. The MSFS folder seems reasonable in size and I’ve looked at every other folder and none seem unreasonably large. Any ideas what may be taking up space. Now I’m concerned about having space to reinstall the MSFS enhancements and updates. Any ideas what might have cause this?
What I didn’t know: the update of windows 10 saved an old copy which doubled the size of the usage on the hard drive. Solved.
To add insult to ijury; the windows update still won’t load.