If a reclaim system is implemented, I doubt SE would give you your gil back directly, since that would flood the economy, and also be a loophole to get around the gil sink if you ever decide you don't want a house anymore.

More than likely if they did this, they'd follow suit of pretty much every MMO I've played that had public housing, which was to give you a voucher for another plot/house of equal value to what you had.