You have 35 days to collect anything that would normally be retrievable from the Resident Caretaker npc after the house is removed by auto-demolition. There's no special handling for mogstation items and after the 35 days, any of them still on the npc will be permanently deleted. If you think you're going to take a long break where your plot may be reclaimed by the server, be sure to place any event/mogstation items in your personal inventory, your chocobo saddlebags or your retainers. Remember that the house storage is attached to the house and items in it will be sent to the resident caretaker as well.