The prime plots definitely won't appear but probably about 90% of the seemingly empty small plots probably would over several months. Why keep a house that's no longer necessary when they can let the plot demo and get back 80% of the gil paid while continuing to operate the workshop.
More importantly, those adding new workshops to their farm or starting a new sub farm would no longer have reason to purchase a plot. It would reduce their start up costs by a fair chunk while any future ward and district additions wouldn't get swamped by the sub farms that have set up new FCs in anticipation.