Well, with the highest temperatures predicted today for any period in the foreseeable future (at 57* at the heat of the day), I followed up on that internal conversation.
The good news is: two hives are still buzzing. The bad news is: my big hive, the one I expected to survive out of the three--is dead. Completely.
I saw a few Verroa mites, but nothing to such a degree that I would say that they had a serious infestation. (Unless that is just a green beekeeper talking.)
I believe that they probably froze to death in some of our recent VERY cold weather. They were situated higher off the ground and with a lot less wind break than the other hives, which would account for their demise and not that of the other two hives.
Anyway, on the off-chance that they were diseased, I decided against putting their honey supers on the other hives. I will extract that and we can eat it. I still have some spring honey left (some of which I just fed to the remaining bees). I have found that plastic zip-lock baggies with honey in them, then pricked with a knife point work tremendously well for in-hive feeding.