How many heals / fortify do you have?
If you enter from inside the keep you will be close to him and can keep him alive. Since everything is targeting him anyway for whatever reason, just keep him buffed up.
If you move a caster to the spot up the ladder right outside that door (make a left when exiting the keep), it will have free reign over pretty much the whole battlefield which will help you control the things trying to kill Cork.
If you're lvl 4+ you can also netherswap him with your tank when he rambos in - it might be enough to draw the archer aggro.
