Around the end of summer, the workers stop supporting the drones as the swarm instinct is diminished and they don't want to waste winter resources on non productive bees. The queen quits laying and at some point the workers actually drive the drones from the hive. I don't know if it's a good sign they are gone right now, but it may predict and early winter. Guess you'll have to wait and see. I wouldn't worry about it though, your bees know what they need and will produce drones when needed. As long as you have brood, things are probably OK!
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