Before the late 80s beekeepers would put a couple supers on in the spring and come back in the fall pull the supers leaving enough honey or syrup for the winter. They would repeat the same process the following year. Pretty simple. Some years they may have had some loses but nothing like today. That all changed in the late 80s when varroa and viruses severely impacted bee health. If mite counts are high at the end of June going into July they are already in trouble even if you treat them. I'm not saying they cant survive but viruses will effect the hive even after the mite population is knocked down. Some side effects in fall are supercedures, poor queens, late swarms, low stores from lack of foragers, sick brood, sick bees, poor brood patterns, unable to cluster or move to name a few. At that point no amount of heating, wrapping, insulating, indoor storing, vivaldi boards, quilt boxes, or feeding is going to save them. Sadly we still don't have vaccines for bees. What we can do is keep low mite counts with a treatment plan that's best for are area along with making and overwintering nucleus colonies. When inspecting a dead out and bees are seen dead in the cells butt out, those are heater bees, the furnace of the hive. They put their head in the cell and vibrate wing muscles keeping the surrounding brood, bees and queen warm between 90-95 F. Honey bees will die trying to keep the hive warm even as the rest of the colony is dying out.