The led device is registered using devm_led_classdev_register so that's automatically cleared when the whole device is unregistered, too bad the led subsystem does turn the led off when the led is unregistered and that causes led_state_set to do queue_work on a workqueue that's already been destroyed in asus_wireless_remove.
Adding a devm_led_classdev_unregister before asus_wireless_remove destroys the workqueue fixes the problem, the other asus wmi drivers may suffer from the same problem though, I didn't really check.