windows 10 (October 2018 update) (version 1809) deleted all my files

"Are you quite sure your regrettable data loss has nothing to do with your own failure to ensure safe and backup on thumb drive, USB-drive, NAS, whatever?"

That's blaming the customer.  Patches shouldn't hurt.  Period.  

 How soon we forget about things like the debacle that was XP SP2 or any of a number of MS failures.  It doesn't make a whit of difference what anyone considers "acceptable," or what "shouldn't" happen if such things do happen. This latest is a particularly egregious failure on Microsoft's part, but to think failures will cease because they "shouldn't" happen is just naive.  Hope for the best, but prepare for the worst.

I too had windows delete all documents and pictures in my account folder.  They are nowhere to be found not in windows.old or anywhere else or recoverable.  Luckily I had a backup from 1 month ago so didn't lose much but seriously why would an update EVER delete personal files?  I had disabled onedrive and uninstalled it from my computer so I assume that was the cause.

Given the number of home users, given the people that have stated to me that they didn't have this setting, this isn't the only trigger.  Home users have no ability to access group policy.

I have rooted my User folders in OneDrive for years without any losses, although the Recycle Bin online has been a safety net several times.

 What I've come to Value equally is Google Drive backup which let's you designate folders to sync to their cloud for up to 15 gigabytes free. 

 I still believe these are essential secondary backup methods because of the very nature of them being fire and theft-proof. I have also pulled out external drives to do a backup several times and found They were dead.

 There is not a day that has passed during the past 10 years in forums that I have not reminded people to backup and still find more than half don't do so, down from about 75% a few years ago.