Thinking more this morning, I have some end-of-season predictions.
First, it's clear that this was the setup for the entire season from episode 3 onward. Maybe initially Bryan Fuller stayed on it wouldn't have been the case. But everything since was set in place by Mirror Lorca as a long con. He somehow came to the Prime Universe. He had knowledge of the mycelial network - probably from Mirror Stamets (the two had to be working together). He then managed to get Prime Stamets onto a ship with a working spore drive, and drafted Prime Burnham out of prison.
Due to this, it would be anticlimactic to get back to Prime next week. There's basically no story left in this season, save for stalling tactics. There's absolutely nothing left for them to do but return to the prime universe, give the Federation the cloaking technology, and work out some sort of armistice - all of which can be dealt with in a few scenes. Thus, I expect that they'll continue to flounder around in the Mirrorverse now until the last episode.
The one other possibility is if the two episodes added late in production were tacked onto the end of the season. If this is true, the season arc essentially ends next week, and we're in for some sort of more self-contained adventure for the last two weeks.