I think the simple and best solution would be to force you off the plot. When you leave a plot, you lose the money. But! If you are forced off due to inactivity for months, meaning not logging in at all, for say 3 months or more, then you would be forced off the plot if there and you would get the money back in the mail. But, the part I have no idea to account for would be the items if someone was furnishing it. Maybe they should keep it if they were?