We wait to check for dead-outs after the snow is all gone (we still have 6 inches on Mount Israel) and wait until days are pretty consistently in the high 50s with no evidence of voiding flights. That being said, we don't want a dead hive lingering in the heat of the day, attracting scavengers or complicating an evaluation of what went wrong; but if you know for sure your colony is gone by this time, here are some recommendations:
• Use a process of elimination to try and understand what happened. Don't assume it was wind, cold, varroa, or starvation. There are some things you can do to try and find out and better your beekeeping skills.
• Varroa counts on the dead cluster - Bees on the bottom board may not provide an accurate picture as we naturally lose about 1/2 of our population in one colony over winter. Try and bush a 1/2 cup of bees off the dead cluster and do a varroa count. A soapy water wash should work. Here's how.
• Save the dead bees! Brush them into a baggie and freeze the bees. We now understand Nosema not to be the threat we initially believed it would be, however, it still can kill. Reach out to me if you want to do a nosema spore count on your dead bees. It could lend some insights. You will need 30 to 60 bees. If nosema is the problem be more careful about how you source your bees. Instructions for spore counting can be found here. If enough are interested we could do this at a club meeting.
• If bees are "just gone" don't assume they have absconded. It probably happened in the fall. Look for the queen somewhere in the combs or debri. In most all cases of absent bees in a northern climate, dwindling-out is the true reason. Dwindling can happen if diseased bees altruistically leave the hive or in the case of fall-mowing, forager casualties. Young bees, aka precocious foragers, will get lost looking for forage that isn't out there trying to pick up the slack, so to speak, and quite literally "dwindle out" leaving only the queen behind.
• Dead bees with heads in the cells does not indicate starvation. Bees crawl into cells and take turns doing so while in a cluster over winter to help meet the heating needs of the colony. If there isn't a large enough cluster and the temperature drops too much, bees fall off the cluster and die. With each layer of bees lost, less bees are able to maintain the heat needs of the colony. A cascade of loss will then occur, leaving the last layer of bees head first in the comb. This indicates too small of a cluster went into winter or it was too cold as moisture from a large cluster's respiration caused hypothermia which can result in the same phenomenon. Insulating hives properly can be a delicate balance. Try and figure out where management changes can make a difference for next winter.
• Once you open the hive that has failed, reassemble it in storage in the same configuration in case the position of the boxes and combs can offer clues as to what happened. Was the cluster far from honey stores? Does it appear brood was started without sufficient bees to cover the brood? Could the presence of brood kept the cluster far from food stores?
• If the loss was not due to disease, frames of honey can be frozen and offered to new colonies. Capped honey does not freeze, but the source of the honey may have resulted in too much crystallization for the bees to process. This can happen with asters, basswood, and canola (high glucose nectar) if they were the only source of nectar available when the bees were making and storing their winter food.
• Don't get discouraged. Look forward to having an abundance of resources to share with your new or surviving colonies. Re-take bee school, enroll in online courses, and in sourcing new bees strive to find bees that have over-wintered in our climate without chemical support to fight varroa. Another option are VSH bees (Varroa Sensative Hygenic) available still from Merrimack Apiaries in Billerica, Massachusetts, about 2 hours from most of us. You can also get on a list for such bees from Hall Apiaries or others working to raise healthy bees or make a plan to raise your own. An interesting new book on this by a UK Bee Club is "The Honey Bee Solution to Varroa, A Practical Guide for Beekeepers".
Hope this is helpful.