I had a brain fart and clicked previous version when I meant to do an update. So it reverted to the version I had a few days ago, and took my save with it. Now maybe it’s my fault for assuming that automatic save backups are on by default, and for assuming that the version would be changed without messing with the saves, but perhaps that functionality should be reworked so it’s not such an easy one-click nuke. The current saves need to be preserved when reverting.
Try looking into recycle bin.
No dice. My second pass found some zipped files that were removed from AppData/temp, but they weren’t it either. It really looks like the current version and saves are completely annihilated when you revert to previous version.
Well, I’ll keep my hands off the launcher code (at least for now), but I might know a way to get your save back, if you are lucky (= got the right system/settings)…
I wish you luck and hope this is of any use for you 
…
If you only clicked on Restore previous version once, your previous previous version, the original with your save game, should be in the previous_version subdirectory. So if you click twice on Restore previous version, you should be back to where you were initially.
The launcher just moves what is in your current game directory to your previous_version subdirectory and vice versa.
Does it make sense?
Good to know. Too bad I didn’t realize the save loss until after I messed around a bunch with updates and manual mod installs to get it to load.
Some more information are provided in the launcher FAQ.