With James Jacobs' take on what may happen if Demogorgon's plan worked, him advancing to another 30 HD, he then squashes Orcus and Graz'zt, Malcanthet has to debase herself for some serious butt smooching, and then Demo challenge Obox-ob and get his butt whipped?
NO WAY!
From the way I see it, I think the Savage Tide AP should end like this: Demogorgon is not only planting these evil black pearls just in the player's world, not in several other worlds as well. The players just managed to stop the tide in their world, but the other worlds get screw (yes but who gives a flying eff)...thus Demo still gets what he wanted in the end.
So, Demogorgon will forevermore still be Prince of Demons. He has Graz'zt become his palace ennuch, Ilsidahur his court jester, Orcus his "royal" chef, and it is time for Malcanthet to be humiliated and degraded: she dropped from consort to slave girl (wearing a dimensional locked neck shackle and decked out in a Princess Leia harem girl outfit).
Finally, Demogorgon takes care of Obox-Ob by turning the entire layer of Zionyn into a roach motel (like what he did with Demonwing).