Heyo! I was also experiencing issues with the Orc King. Dying and restarting didn't help, and closing the game to try again wasn't helping either.
I noticed that every time I saved the King for last and killed all of the other orcs, the King wouldn't die. But when I focused him down and ignored the others I managed to kill him. Don't know if this information helps, but figured I'd throw my own experience out here just in case it does.
Overall loving the game!