User Crash, but old user data is (seemingly) still on HD? So our late 2015 iMac locked up the other day, and I had to restart it.  My wife and I both use the computer, both with our own (both admin) users.  I was logged in on my user when the machines crashes.  After the restart, the computer booted to the user login screen, only my wife's user showed - mine was gone.  Logging in on hers, it looks like my user is just "gone" - doesn't show in System Preferences.  However, when I go to /Users, there is a folder with the my user name, but very little data in it.

But I have hope that somehow, somewhere, my files remain?

Our 1.02 TB HD is 98 GB away from capacity.  My wife's entire user is only 432 GB.  So there's a missing 500ish GB.... that would seemingly line up my missing user and data.

Apple advised me to update to Catalina (hadn't gotten around to it yet), which I did, but that didn't bring anything back.  Obviously restoring the user would be ideal, but really all I care about is my music, pictures, etc.  Anyone have any idea on how to get at that information, that is still seemingly on the HD?
Questionable advice from apple.  I suspect you do not have a backup of your data. You should have a backup of all your data.  Since you do not have a backup, this implies you do not have administrator level knowledge of macOS. You best find a professional to look for your data. 

If you really, really need your data, you need professional help. One of the best professional restorers is "drivesavers.com".  

This isn't a good time to be running around trying to fix your computer.  The best advice is to buy a new computer and wait until it is safe to go out. Another good advice, is to buy an external drive and run from the external drive. An external SSD from OWC is what I'm running on now. Here is what I am using for my startup drive: https://eshop.macsales.com/item/OWC/ME3NH7T00/  plus https://eshop.macsales.com/shop/SSD/OWC/Mercury_6G/

You should use the terminal to look around the root of the harddrive, / and the user directory /Users. The thing is the more you use your machine the less likely you will be able to recover your data. https://discussions.apple.com/docs/DOC-11071  Please post back the result of:

ls -l /Users


While requiring administrator knowledge of the mac, you can try:


Immediately backup your wife's data
You should try cloning the drive of your machine 
You should try all data recovery on the clone of your drive. 
get an external drive
install macos on the external drive
try to find a data recovery app that will get back your data


a bunch of data recovery tools:

Perhaps Disk Warrior will be of some help:
http://www.alsoft.com/DiskWarrior/

"Stellar Phoenix Macintosh - Mac data recovery software, recovers data from damaged, deleted, or corrupted volumes and even from initialized disks."
They have a trial version, so I guess you can see if your data can be recovered...
http://www.stellarinfo.com/mac-data-recovery.htm

"Data Rescue II is the best data recovery software on the market for recovering files from a problem hard drive. Data Rescue II works when other tools fail. Data Rescue II is also completely safe to use since it does not attempt any risky repairs to the drive while its scanning."
http://www.prosofteng.com/products/data_rescue.php

FileSalvage is an extremely powerful Macintosh application for exploring and recovering deleted files from a drive or volume.  FileSalvage is designed to restore files that have:
-- been accidentally deleted.
-- become unreadable due to media faults.
-- been stored on a drive before it was re-initialized/formatted.

http://subrosasoft.com/OSXSoftware/index.php?main_page=product_info&amp;products_id=1

"TestDisk is a free data recovery utility. It was primarily designed to help recover lost data storage partitions and/or make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally erasing a partition table)."
http://en.wikipedia.org/wiki/TestDisk

Wondershare Data Recovery for Mac

"Recover lost photos, video, documents, email and archive files from any Mac-based hard drive or external hard drive, iPod, USB drive, SD card, digital camera, mobile phone, and MP3/MP4 player, due to accidental deleting, formatting, virus infection, improper operation, unexpected power failure, and other unknown reasons. Also, iPhone recovery allows you to recover lost photos, videos, SMS, contacts, note, calendar and call history from iTunes backup file. With the free trial, you can preview all your recovered images, videos, music, documents and archive files prior purchasing this Mac Data Recovery."
http://software.bigbigsoft.com/data-recovery-mac

"If there is any chance of recovery at all your best bet is Prosoft Data Recovery." by macjack

https://www.prosofteng.com/datarescue-mac-data-recovery/

Eric Root's list:

https://discussions.apple.com/message/30259740#message30259740

Chterando's list:

https://discussions.apple.com/message/31780403#message31780403