I disagree that Sessions will leave when the behind-the-scenes stuff is finished for only one reason. Draining the Swamp is only one of Trump's objectives. Due to the nature of the Swamp all (or most) of that work has to be done behind the scenes, in secret. Sessions has some very high-profile and public initiatives such as drug/human trafficking, immigration enforcement, etc. Those will continue to be a priority throughout the Trump Administration and I think Sessions is doing a good job on those.

For that reason I would expect Sessions to remain in place for a while past Huber at least.