Hi Marco,
no, there are no .tmp files left. Today, I lost half of another Workset, but not during windows restart. I closed (on multiple PL/SQL Developers simultaneously running) all Worksets with Close button. Then restarted PC and opened again. Half of windows in workset said "Error reading file" and windows were empty. I saw only half of files in AppData/Roaming/../Worksets/Worksetname .... (and no .tmp files at all). After clicking on empty windows, desktop.0XX files has been created with zero size on FS, oops.

See screenshot.
Best Regards,
Stanislav