While I was tempted to take the cowardly way out, my inner Scappy Do took over.
So I backpedled through various enviornments firing at range and dropped a fireball scroll on him when he started to wear me down so my dragon stone is just waiting for the quest.
A useful lesson from other people's experience is that if you want acheivement, play online. I am not sure I do but have a tendancy to try to fix any bug I encounter. 
The bleak falls barrow achieve is for the quest of that name, not just completing the dungeon. Pretty positive you'll still get it
