Hmm...that would be the true ending...and the true ending XD. I got the sketch and saved the game before getting to the ending part, so I was able to load it and try all 3 choices. And I might read a little bit of the walkthrough, heheh.
After seeing the 3 endings and comparing them, I decided the true ending suits the story best. In my opinion. Gareth and Zakhari hate each other, but there was love remaining in both of them as well. So playing as Aidan, an outsider, I think it's better to let them deal with their complicated relationship themselves. And that leads to the true ending.
And btw, there was a little bug here, idk whether you have fixed it or not...I collected the complete sktech in the 2nd room on the 3rd floor without getting the torn piece in Gareth's room, because I went to the room with a hammer first XD maybe you need to check if the player has the other piece first.