I know this has been probably asked asked to death at this point, but did they ever talk details about why Sierra left? They did Noxian Nights together as well, right? That seemed to have worked out. Wonder what happened here.
Of course they didn't talk about it publically, but probably in the realm of creative differences and work ethics.
If you look at the games Sierra Lee has put out it seems evident she's probably not interested in writing "female rapebait" stories, which is the demand KoD started increasingly trying to appeal to.
Sierra Lee also has finished multiple decently-sized games since she stopped working on KoD and is close to finishing her main game which is easily 200+ hours long and has been in development for over 10 years. I can see why someone like that wouldn't feel comfortable with KoD's pace of constant delays and struggling to deliver 1 decently sized update a year.
Nomo always had the creative lead on Hreinn Games, Sierra Lee was the hired work to put together the writing and gameplay design. Noxian Nights probably only happened the way it did because at the time Sierra Lee wanted to network more with other porn game devs and get more experience/exposure, but then she got too big to make any sense for her to continue working in other people's games, specially if they weren't something she was interested in working with.