You have to fight Samuel's DK's in order to trigger the cutscene at the smith's door to get entry. You can cheat to bypass the door (either with the procedure in the armoury trick post (link above) or by
hex teleporting). I don't know if that will work with the smith, but it will get you access to the stairs in the room close to Samuel's lair that lead to the exit.
Are the DK guards really that tough? Give the summoning doll a crossbow and one character a bow or crossbow, set them to aggressive, and have the other character run around distracting the guards. If you keep moving the character shouldn't get hit very often, and the other characters will eventually be able to take down the DK guards.
