In a real estate system like we have here it's simply unfair for people that aren't using the land to be permitted to keep it. If someone doesn't log in for ages they should lose the plot and be given a voucher of some kind that would let them re-purchase that or a same sized plot when they return. The amount of time necessary for this to happen should be set quite high... say maybe 90 days or something? If anyone is gone from the game for more than 90 days there are hundreds of other players in the game that would make better use of that plot. The player losing the house wouldn't really lose any gil either, as they'd be able to re-acquire a similar plot later if they ever returned to the game.