I'm aware that sometimes a user will delete their question as soon as they get a useful answer, to hide their tracks. Sometimes I spend time contributing an answer, and it bothers me when my work is erased, not because it's not useful, but because it is useful.
Here's an example, although not affecting me: This question was upvoted, and garnered two answers. One of those answers was also upvoted. Three minutes after a possible duplicate was pointed out, the user deleted the question.
I was under the impression that the questioner couldn't delete their question if it received upvoted answers. I guess I was wrong. What is the policy for real?