Okay, so players go inactive all the time from servers. Maybe they had diamond or iron, or other precious resources. Those are now lost from the map. You'll never be able to use them, since that player probably isn't coming back. My idea for a mod would be one that would, for example, take all the items of every player inactive for a couple weeks, and put it in the nearest chest to where they were located. You should of course be able to set this mod, and it should run periodically.