It happends, not sure if its often. I'm not realy a person who checks every house sign to see if a house is in IDOC.
Every item in the house is freely lootable. First come first serve!
Personal i'm not a fan of IDOC's. I know alot of people want to shoot me what i'm going to say. But i believe when a house dissapear all items should dissapear with it. I believe that all items can be got one way or another, alone or not, trough normal gameplay. And it can't hurt now and then to let items/gold dissapear from the shards.