I had a similar experience with leveling a prot pally. I entered DTK with everything killed up to King Dred. A level 80 hunter was trying to tame him with his level 75 buddy of his from the same guild. So he asked me to not focus on him and he would attempt to tame him. I said whatever and just watched him try to tame him. A wipe later, I just left. I didn't want to get stuck with an avoidable repair bill because he was persistant on taming King Dred. No wonder the prior tank had left.
My point is, you don't always get what you want in a instance but you always do have the option to leave and come back later when the debuff wears off.