No. The only time a thread will be closed (other than if it turns into a flamewar or has a lot of spam in it) is if someone decides to come along and post in it after a month has passed. For example, if no one posts in it after the post I just made and if someone comes along and finally posts something on January 25, it will be closed. This is because it would have been over one month from the last post in that thread (made December 21) and the new post someone makes (which would be dated January 25).
The exception is if it's a story thread in the main writing forum, and you, the writer, post in it to put up a new chapter. For example, I can post in my own story thread, even if the last post was made in October, so long as my post contains a chapter. That's because I'm the author. However, a reviewer can't come in and bump the thread because it's been over a month since the last post. Get what I'm saying?
Incidentally, I would suggest starting a story thread in the main forum anyway. It sounds like you've actually started a story by now (as opposed to discussing and planning it), and you would probably want the protection I mentioned above.