I made sure to hit him as fast as possible so his healing could not compete, and he went down quite quickly. He didn't even break off any shards.
Try it solo with your Champ, it may just work? Oh yes, you can skirt around a lot of the mobs on the way to him by hugging the island walls, so you only have to deal with the bridges - it will knock a lot of time off the instance. I think I did it in about an hour that way.
Be warned - once you kill him and talk to Sgathan, he will give you a nasty surprise, so heal/med up before talking to him
