我没有测试这个，但应该可以：

function check_post_attachments($post_id, $post){
  if(empty(get_posts(array(\'post_type\' => \'attachment\', \'post_parent\' => $post_id)))){
     $post[\'post_status\'] = \'draft\';
     wp_update_post($post);
  }
}

add_action(\'save_post\', \'check_post_attachments\');