I heard from my editor today, who told me the cover scene had been chosen. It was one of the scenes I suggested, with a slight change to it.
My original thought was that, if they wanted a "minimalist" look, they could use the black door where books of forbidden black magic are kept that the main character steals in an attempt to summon a long-dead wizard from the grave to learn the location of a lost library of knowledge. The door is inscribed in gold with the wizard symbol for death, and protected by powerful spells to keep people out. They loved the scene, but thought it needed the main character in view as well. The symbol of death may be embossed and foiled, which I think would be pretty dramatic and eye-catching.