I have similiar problem with a Demon: The Fallen campaign that I'm running once every two weeks. The whole setting has gone to ****, so I really don't like it anymore.
What I did was cut a whole Story out of the campaign. So, now instead of having to come up with about half a year more material that I know I will hate I'm going to play with them for a little while longer, and then present them with a BBEG that will slay the whole party. Well, the characters may succeed in taking the BBEG down with them, but that's the best I will offer them.
They will be upset, but I'm done with the campaign. A wrote a good campaign, but after I started running it I just lost the point of why I'm doing this?
So, if you feel like retiring your campaign, then I would suggest giving it some kind of a (at least partially) satisfying conclusion. Less people are going to hate you for it, and some might even respect you for hanging in there until the end. Even if it came a little early for their taste.