A sensor system for a critical system, when designed, should have some 'failsafe' wherein the loss of the physical 'sensor' or it's electrical connection does not yield a reading that might represent a *nominal*, in range or safe reading.
So, some provision must be made to indicate that an actual 'sensor', be it light (photodiode, photocell, etc) heat (PN junction, Thermistor or thermocouple, etc) when open other otherwise disconnected (failed) indicates to the data mux (multiplexer) that said sensor is truly in a 'failed state' and cannot be relied upon for meaningful data ...
How this is specifically accomplished differs from sensor to sensor, but, it sounds as if these temp mmst devices aboard the SS were in some sort of 'bridge' where the physical loss of any element in that 'bridge' can truly result in offscale readings ...