The possibility may be unlikely, but the point is that a person should be able to rely on being made aware that his system has lost one, or more, of the sensors.
Otherwise you could lose, and then regain, contact and never be aware that your system is totally unreliable. As I've said before: a system that takes an hour to make you aware that a sensor has lost contact is bordering on useless. That's almost like having a oil pressure sensor that may quit working, but you won't know it for an hour. To me that makes that oil pressure sensor a pretty useless instrument.