Since I wear softshell pants most of the time, I carry my hardshell pants for emergencies in the winter, although they are often the last thing to make the cut into my pack (I don't like the extra weight). I don't carry fleece or any other insulated pant, although would do that for planned winter camping. The cocoon pants on BPL would be very nice and warm for the weight (so if I was buying, that is what I would be looking at first).
I don't carry a sleeping bag either, and for an extra 2 lbs over the weight of the insulated pants, I would think that would be much, much better in an emergency. I would probably go for the bag for trips with more exposure or risk (like the Daks with no cell phone coverage, or the whites, above treeline).
One of the problems with pants is actually using them in an emergency. They probably need full zips to get them on reasonably. With a broken leg, it would be almost impossible without zips and still pretty hard depending on how bad you were.
This may not be rational, but on bigger trips I will often bring a back up pair of wool socks (mostly for my feet if I need them), and figure if I really was in my bivy sack trapped for the night, I could cut the toes off and pull them on as leg warmers.