Your house will be relinquished pretty much. Right now there is no way to get back the money you used to purchase a plot. Its pretty much a sunk cost.

Unless you "sell" the plot to another person, where they pay you a certain amount of Gil, then you relinquish your plot and then they pay the full purchase price for the plot again, but don't think may people will do this since they will pretty much pay double, they might as well just buy a medium house at this point, assuming you have a small house.