Liberty Ridge on the north side of Mt. Ranier is one of the most difficult routes on the mountain. It is a very steep ridge and often avalanches, falling ice and rock are a constant hazard to any climber on the route, even during perfect weather. The likely cause of this climbers hypothermia is that commonly mountaineers on routes like Liberty Ridge will pack a minimum sleeping arrangement to save weight. Perhaps a good down parka and a "half bag" setup or even less. This is a long climb, one way up and another way down thus every item must be carried to the summit, no leaving items behind at a high camp. It is considered too difficult a route to downclimb. It has been done but I am sure not by intention.
Best wishes for a happy outcome to the fate of this climber. Doubt it will be though.