The official FAQ post on meta.SE about how deleting works.The official FAQ post on meta.SE about how deleting works. The first answers includes the rules for automatic deletion, and links to more detailed explanations given in the next reference.
The post on meta.SE that most clearly states when "bad" posts are automatically deleted.The post on meta.SE that most clearly states when "bad" posts are automatically deleted. This includes a new rule for automatic deletion that was added in June 2013.
Since the automatic delete rules mention locked questions, here's the official FAQ post on those.locked questions, here's the official FAQ post on those.
Duplicates
My post on meta.SE asking if the auto-delete rules apply to questions closed as duplicates is the closest thing there is to an official answer.My post on meta.SE asking if the auto-delete rules apply to questions closed as duplicates is the closest thing there is to an official answer. And the answer is: Duplicates do vanish, so the auto-delete rules apparently apply.
This isn't official since there's nothing posted by SE employees, but it explains what the observed behaviour is: the same autodelete rules apply to questions closed as duplicates. There's a link to Shog9's answer to another question that implies that crappy duplicates deserve to be deleted.to Shog9's answer to another question that implies that crappy duplicates deserve to be deleted.
