Finished Anihilation, starting Authority. Your fantasyscape reminds me of this thing I'm learning about called dark green environmentalism... That and the movie Avatar.
What do you think about happy endings?
Happy endings have to be thought of terms of the rest of the novel or series. An unearned happy ending isn't particularly satisfying for the reader. But on the other hand unrelieved pessimism and darkness can be, for lack of another word, boring. I think if you follow the character arcs of the people in your work properly, you can get to a place where each person winds up where they should have ended up, and the effect of the whole is something nuanced. Which is to say, some happy endings are actually half-sad endings where you're surprised it's turned out as well as it has!