The last one I ran ended at 20th. The party destroyed a number of obscure demon lords who were part of a lich's attempt to steal souls frozen in the ice of Stygia in the Hells (the demon lords, such as Azuvidexus and Bechard, were all forced into service by the lich, who had their true names). Several pit fiends, Amon, and Geryon also got slain. The Oath of Vengeance Paladin became the new Archduke of Stygia while the wizard decided to try becoming a demon lord in the Abyss.
My current campaign is at 9th so far.