Looks like when one player leaves the party then one of the Phantoms will "crash". But other Phantom will "work". It can't even die(http://steamcommunity.com/sharedfiles/filedetails/?id=740511650). Looks like it can't happen with all the Phantoms at the same time(http://steamcommunity.com/sharedfiles/filedetails/?id=740511843). They still have teleportation ability(http://steamcommunity.com/sharedfiles/filedetails/?id=740512213). Once again that woun't happen with other Phantom(http://steamcommunity.com/sharedfiles/filedetails/?id=740512370).