I decided to uninstall the game (making sure of not uninstalling save files) to reinstall on a SSD.
But now, the saves are gone. The game remembers my sound and video settings, though.

How can I retrieve the save files? I suppose the demo doesn't have cloud saving and I surely hope the uninstaller didn't remove them without my consent...

Not sure where the save games are stored. However, I had problems with quicksaves not saving rather often in the demo. Also, the "last save timer" seems to malfunction as it was giving me 5-minute warnings from the last save point when it was clearly less than 5 minutes. Maybe that was because the quicksaves were not saving correctly?

On my machine the save files are in the directory "C:\user"

I found this out by using SysInternals Process Monitor -- I added a filter for [Path - contains - "save"], and saved in game.

I was able to transfer my collected badges from the demo to the actual game by copying (and replacing) the file "C:\user\userData.save" to "C:\Users\<yourUser>\AppData\Local\Desperados III\<userSomethingSomething>\userData.save"
[EDIT: note that this will blow out whatever progress you've made in the actual game. make a backup copy of your save data before copying and replacing]

I was able to load the save I had at the end of Flagstone and complete Flagstone. Everything seems fine so far!

I take no responsibility if this messes something up for us down the road :)

[EDIT 2: This copying of save files from the demo version to the actual game seems to have some problems. After completion of the next mission, the game froze trying to bring up the 'Replay' screen. The .exe was looking for a GameProgression.dll and a gameProgressionTemp.rply (or something similar), neither of which seem to exist in the actual game files. So it seems that the way replays are handled changed a bit and the demo save files aren't compatible with that change.

I'm restoring my save files from the backup I made before trying all this. :) oh well

I wish there was a way to keep the badges I acquired in the demo version. Not a big deal though.]