Kristian: I didn't buy that promo, yet I lost Dark Fall 2.
It doesn't matter when you purchased it, because GOG has been suffering from a really annoying bug for a long time now that temporarily removes a game from one's account, when said game is removed from the catalog. It has happened at the very least with the Bohemia games, with the first Nordic departure, with Blade of Darkness and now, with the second Nordic departure. I bought only 2 games from the latest Nordic promo, but for a while all my 15+ Nordic games were removed by my account, even games that I had well before the first removal. Since game restoration happens manually, the biggest probability is that the GOG staff has forgotten to restore the game.