I sent GOG a ticket about this on September 15th, and support responded the next day on the 16th telling me they will look into it.
If the Heroes dlc isn't released by October 31st next month, I doubt it will ever release on GOG.
Dekovir Entertainment doesn't seem to care about their GOG customers. What else is new?!
@Truth437 I know that my statement will differ slightly from the basic topic, but enough silence: This is not only a problem of Craft The World, but recently I have noticed that a lot of game distributors do not take GOG seriously - an example is that a lot of games (here) there are not many language localizations, and for example on Steam (if you compare), there are often a huge number of translations in games in their productions (you even find a lot of Asian languages). Here only conservatively English, Spanish, French, German, Italian.
So you have to think about whether GOG will accept complaints about refunds for productions that have stopped being updated here and whether it will remove such productions from its store.