We had one this winter, and I believe they froze. The cluster was small, and this particular hive has wintered prior years in a cluster much smaller than the rest of our hives. When I opened it up after they died, lots of bees headfirst in the comb, both sides, in the area where they were clustered. The edge of the cluster had dead bees on top of capped honey. They seemed to be doing the same as last year, right up until we had a weeklong stretch of -15C, much colder and longer than we've seen in the prior years. They were in contact with honey, and died head first in cells. I dont think they starved.