If you have regular backups of your system, it'll be easy to find any temporary files left over by Mathematica by comparing directory listings pre- and post-incident.

On Windows, if you're using a backup system that can mount the backup images as volumes - e.g. Macrium Reflect - you can get the directory listing of the temporary folder:

% on the backup image volume, let's say it's D:
cd d:\Users\%username%\
dir d: /s /b sortorder:N > %userprofile%\temp_pre.txt
% same on the main volume, say it's C:
cd %userprofile%
dir c: /s /b sortorder:N > %userprofile%\temp_post.txt

Then you can use your favorite file differentiating tool to compare the two files and see if you can spot anything useful. SmartSynchronize is "free-to-use" (and otherwise well worth the money), and cross platform, so you can use that to inspect a user-friendly difference of the two directory listings.

Of course, you could do all that in Wolfram language as well.

That seems to me to be a big bug!!! How many lost hours of work this has cost people is probably staggering. Why not have some sort of recovery capability. Many other programs can do this so why not Mathematica??? From simple apps like Notes to sophisticated ones like Photoshop.

Why in the world has this never been addressed??

Thanks...