In a monitored approach (for a two crew operation) the landing pilot, who is the monitoring pilot - i.e. NHP for the instrument part of the approach - makes the decision. As the aircraft approaches the decision point, the HP will call 'decide'; in the absence of a response from the landing pilot, the HP will initiate a go-around. In airlines, the landing pilot (monitoring pilot) is usually the PIC - this makes for better decision making (for obvious reasons).
I have done this when I flew for TWA. I can tell you on a CAT III approach, you "may" touchdown on a go around at 50'. BTW...IMO, the monitored approach is THE safest low visibility approach method in a two person crew. For us, as a First Officer flying the aircraft, if you didn't hear "I've got it" or "approach lights" you commenced the go around at DA in a monitored approach.