Ok, here's my situation and I'd like to hear what a publisher thinks. I have written two books out of a four part series (four parts that I planned to write originally). These books are non-fiction books and each stands on it's own. My problem is that I've lost interest in writing the rest of the books and am dragging my feet on writing the final two. I did not sign a contract with my publisher for the whole series, only for each book. However, they know that I planned to write four books. The books are selling well (for LDS standards), but like I said, I have lost my desire to write them. However, I am still interested in writing other books and having them published by the same publisher.
If I were to not finish the series, would you recommend I contact the publisher to let them know or do I just not send in any more manuscriputs? And if I do this, can you tell me how this look to the publisher? Am I kissing my lucrative (ha ha) writing career goodbye?
Or would you recommend that I buck up and force myself to write something I have no interest in anymore? Should I stress myself out and spend hours and hours of work just to finish the series on time?
You have to deal with this up front and in a professional manner or you're shooting yourself in the foot. Your publisher has invested money in this series, with the idea that it's going to be a series. If you just don't ever send another manuscript, it's going to look like you're a flake.
Call your publisher today and have a chat about it. Ask them how the series is going and if they want the other two books. Maybe they'll say they think the "series" has run its course and won't be interested in the next two books. Or maybe they'll only want one of them. It's okay for you to admit that you're losing the thrill of this series--that happens a lot, even in fiction (Can we say "Robert Jordan?" RIP), but be prepared to pitch them something else to replace it.
However, if they say yes, they want the other two books, then you've got to buck up and do them. And you have to do a good job of it, as well, or they won't trust you for any future book series that you pitch them.