I took him and his buddies out as a mage. If you have access to a level 3 Unrelenting Force things become simple because if you Shout them they will fall down the stairs and probably die. I don't recall if you can shout him off of the stairs completely, though... huh. Now I'm curious.
I went straight for him and killed him asap, had to use whirlwind sprint to get to him quick. then i just used heals until i was rescued by azura / that mage guy