Original team was Nomo and Sierra Lee. Nomo does art, character design, and story concept. Sierra did writing, game design, and some coding. Sierra left for unknown reasons, we don't know anything except that it was in amicable terms (so it could be anything from creative differences to her just wanting more time to work on her own projects). Since then, Nomo hired 2 people to replace Sierra Lee, a writer and a coder, not sure who's doing game design.
This has all happened over a year ago, so honestly it shouldn't be much of a factor when discussing KoD's current development. At most it just serves as confirmation that the bottleneck of the game's development is Nomo's work, so either he needs to delegate more tasks or find a way to speed-up his art, hopefully without losing too much of the quality he is known for.