Everyone is quite keen to "prove" whether or not the crew could have safely climbed to safety altitude. Most of us who have spent many hours in cloud know that it is a very variable and unpredictable phenomenon. Cloud type, water droplet size, terrain mixing, aircraft speed, blade angles, inlet design etc etc etc, would all have had an effect on how that particular aircraft would have iced up on that particular occasion. Had they attempted to climb (anyone established they didn't?), they could have hit severe iceing at 500', 10000' or not at all. 1.98 degree lapse rates only occur in the theoetical world.