All of it was done by several artists. Some left, some stay. I don't know who worked on specifics but I think like 90% of the 2D (incl. icons, codex, UI elements) was done by the concept department. They are all so incredibly talented and consistent in following chosen art styles that I cannot distinguish work of one from another.That's our current lead graphics artist. Seeing shit is his job.
Also, coincidentally, he's the person who made the Sassau monastery.
Is the artist responsible for the 2D graphics (the map, book illuminations, monastery wall paintings etc.) still with you? If so pay him with gold, coke and hookers, don't let him leave.
If I'm not mistaken the map was largely done by our former art director and concept lead Miki Podrocký. He left like a year after release.