I go with wear and tear. An old forager loads up with nectar or pollen, struggles to get airborne, fights wind and distance, perhaps cold and simply runs out of gas. Two years ago I was researching a paper while sitting in front of the hive. A bee hit my leg and fell to the ground. I watched and waited as she crawled around, then hovered an inch or so off the ground. I picked her up and found her wings completely frayed. She hardly moved. I went in the house, put a drop of honey on my finger and let her take some. Within a couple of minutes, she took off, circled a few times and then clumsily made it to the landing board. I think she was out of fuel, having worked so hard to make it back. The morning temps weren't the best either. I probably saw her last flight home.
"My wife always wanted girls. Just not thousands and thousands of them......"