>doing well in adventure so far
>group collectively takes notes and reasonable speculations for the investigation, undertakes sensible actions to advance the plotline
>party defeats enemies in combat with ease, and rolls splendidly on all kinds of noncombat tasks
>end of last session
>GM announces that because of our own actions, we have hit the bad ending and unleashed the evil gods, destroying a country and possibly dooming the world
>GM will be unavailable for a while to explain or answer questions
How do you cope with this? I strongly dislike the "Protagonists are the ones to unleash an ancient evil on the world, and now the rest of the story is about the protagonists cleaning up their own mess" plot in any form of media, because it implies that the world would have been better off with the protagonists dead from the beginning, and I just dislike that.
I told the GM from the beginning that I preferred "heroic, high-spirited, light-hearted, optimistic, hopeful fantasy that can still get serious on occasion" too.