It won't be removed, however if you do it before 6.0 you'll be rewarded with a Feat of Strength and a title "of the Black Harvest". If you do it after 6.0/pre-patch is released, you won't get the feat of strength.
I checked last night. The fight seems to have been scaled. The bosses new HP is 1.5 million and at 91 it takes about the same time to burst him down and his abilities hit HARD even then. Probably will change at 100, but i dont have a toon near that.