Certainly nothing good for anyone,ancient elves included.
Can't he simply remain in the fade to play with spirits like he did for all of these millenia?
My first impression on the Dread wolf on DAO back in 2009:
was the idea of a powerful being who tricked for whatever reason(rule in a world full of ignorance and without the other gods) the others "gods" and decided to live by seeing with satisfaction the actions of his misdeeds that proved him to be a more competent god than the others.
Fen Harel in DAO was complete,accepted by both the Evanuris and the forgotten ones
(now i know it is only because he was with anyone side but his own)
but in DAO i really thought that this creature was the reason as for why Thedas was shaped (which is true) bu he did that on purpose while at the same time whispering into the hears of the human magister to enter the black city in order to use the taint as a weapon to kill all the forgotten ones who were dormant in the forms of the old gods,by turning them into archdemons,and later by creating the Grey wardens to "save the world" from those creatures came out of a shakespearean tragedy novel of betrayal..
When an archdemon was dying because of a GW sacrifice, I could have imagined that he was laughing somewhere in the fade because another god was removed from the world,and he was waiting until each of them would have died
(now i know that this was not his plan,he do not even care much for them,is all about Mythal for him) only then he would have presented himself as the only true god of the world,when the ignorants people who forogt all the ancient mysteries and power thanks to his misdeeds would have been a no match for him.
On the paper he was the most fascinating piece of lore of the franchise.
What i got in DAI,was instead a frustrated bad elf,polite but also insane who didn't really knew what he wanted and was dumb enought to grant to a magister his powers wihtout informing himself prior of such magister ability.