I had some bad driver issues that led to me need to 'reset' Windows from the local recovery partition. This recovered my machine and got it bootable again. Afterwards, WSL2 wasn't installed, so I tried to install it. It rebooted, etc, then fetched Ubuntu 22.04 from the Microsoft Store as usual. However, instead of keeping my previous WSL2 content it started a new user:
Ubuntu is already installed.
Launching Ubuntu...
Installing, this may take a few minutes...
Please create a default UNIX user account. The username does not need to match your Windows username.
For more information visit: https://aka.ms/wslusers
Enter new UNIX username:
Sure enough, the VHDX was new, only 1GB:
Directory: C:\Users\patrick.lang\AppData\local\Packages\CanonicalGroupLimited.Ubuntu_79rhkp1fndgsc\LocalState
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 11/20/2023 9:03 PM 1200619520 ext4.vhdx
I know that user profiles are temporarily stored in c:\Windows.old\Users so I went for a delve there. I found a LocalState folder of the same name, with a VHDX much bigger than that at C:\Windows.old\Users\patrick.lang\AppData\Local\packages\CanonicalGroupLimited.Ubuntu22.04LTS_79rhkp1fndgsc\LocalState
I finished up setting up the "new" Ubuntu instance, then ran these steps
cd C:\Users\patrick.lang\AppData\Local\packages\CanonicalGroupLimited.Ubuntu_79rhkp1fndgsc\LocalState
wsl.exe --shutdown
rm .\ext4.vhdx
mv 'C:\Windows.old\Users\patrick.lang\AppData\Local\packages\CanonicalGroupLimited.Ubuntu22.04LTS_79rhkp1fndgsc\LocalState\ext4.vhdx' .
After that, running "Ubuntu" via the Windows Terminal menu started up the instance with my old data intact.