The Balrog vs The Witch King

Originally Posted by obloquy

He may not have reason to be sympathetic, but that alone does not provide a reason for him to be hostile.

So, in effect you are saying the two could have coexisted. The Witch King & the Mouth of Sauron, for example, managed to do it. The difference here though is that both were in the service of Sauron, & their rank was clear. The Balrog had been at rest in Moria for a number of years without any call from Sauron, so how may one decide whether he still had allegiance to him?