This article describes what you should have done before selling your AirPods.
Before you sell, give away, return, or recycle your AirPods - Apple Support.
If I am understanding the article correctly, the AirPods do not have to be connected to Bluetooth so you may still be able to disconnect them. Otherwise, the new owner will not be able to use them as "AirPods can be paired with only one Apple Account at a time. You need to remove AirPods from your Apple Account before giving away or selling them. That way, the new owner can pair them to their Apple Account." Good luck.