This is pretty easy. The thing I had in my mind was somthing where when a demon prince is deposed the deposer starts off as himself, but eventually turns into the demon prince he just deposed. The universe needs orcus, so the demon that just deposed orcus becomes orcus. At firs it looks like an identity crisis, and thats what the balor thought it might be, but that second identity gets stronger, and his head starts to get more goatlike, but he figures, "who cares, after all, I took Orcus' place why can't I BE Orcus." He gets fatter, and more goat like, and then to his horror, he realises that he is not himself. Soon the deposing balor is just a memory. After seeing this happen a couple of times most demons won't raise a hand against the princes because they do not want to loose their own identity.
Imagine a cocky balor taking down juiblex only to slowly melt into the a jibbering and jabbering mad lord of oozes. As the process begins, his likes start to change, little things first, then more knowledge than he ever knew, then a new second personality that slowly takes over from the first. He seeks to escape, to adbicate his new throne, he seeks to have anyone replace him, they all bow to him and refuse. Feeling his slowly disolving mind and sense of self, he is filled with utter fear as his new minions start to refer to him as Lord Juiblex. Juiblex sits in power once more.