Your northern neighbor says not long!
This kind of sustained cold takes a heavy toll on the bees unless everything is perfect in your hives. Unfortunately that is not usually the case. I've had plenty of dead outs with honey still in the hive. When it's this cold for this long (3 of the Great Lakes completely iced over), it can get too cold to move to new stores and they simply freeze to death. The smaller the colony the quicker they tend to freeze out. Anything you can do to keep the extreme cold off the bees is good.