With the GOG version, the Galaxy client can be set to sync saves online. I don't recall if that is enabled or disabled by default.
In Galaxy, if you select the game, click More and select 'Backups & goodies', there is a 'Cloud saves backup Copy' section to (I assume) download any saves that are online.
Do you have any backups of your My Documents folder? If so you may be able to restore a previous version of the save, if not the most recent.