Good luck, but if you do need to fight the boss feller again I strongly recommend getting stuck in hard and fast. You know where he is going to be popping up from so be there waiting with melee weapon(s) out, as soon as he starts getting out of his box charge in swinging and don't stop until he is dead. This is no time for fancy foot work and at low level archery or ranged magic ain't going to do enough damage, so get in there and give him lots.

With Bethesda games you learn to save often, very often. I know it's kind of a nuissance to pause and save all the time but it got me out of countless sticky situations not just in Skyrim but in all the Elder Scrolls and Fallout games. I recommend saving before entering through doors that require a loading screen. When I was working through the quest Forbidden Legend I wasn't able to loot one of the draugr bodies to get an important and vital quest item. I had one save right before I began fighting that particular draugr and another right before I entered the room he was in, which led to a loading screen upon entry to the room. After reloading the save where I was in the room and killing the boss draugr over and over again I still couldn't loot him. I then learned that it wasn't a save that had to be reloaded, it was the entire room that had to be rebooted and reset. Luckily I had a save right before entering the room. I loaded it, entered the room, watched the loading screen and successfully killed the draugr and was able to loot his body with no more problems.

I save so often it's almost laughable. On any toon I start, by the time I'm in Bleak Falls I've already usually got 140 saves....