In this meta post, Shog9 writes:
But don't delete duplicates
Seriously, don't. Unless they're literally word-for-word duplicates, just leave them be - folks tend to find all sorts of different ways of asking the same questions, and the more variations we have pointing to the same canonical answer, the better. Of course, you should
However, this seems to be at odds with the current auto-deletion policy, which makes no exception for dupe-closed questions that meet Jeff Atwood’s auto-deletion criteria for closed questions, which includes being closed, having a negative vote total, and having no answers. There are other ways for them to be auto-deleted, but that is the fastest one.
When ЯegDwight asked Grace in chat why this is so, Grace reported that fixing it would make a pretty good feature request:
So I am making that feature-request: I propose that questions closed as dupes not be subject to auto-deletion. The current process works against the idea of duplicates providing “many paths” that lead to the right question, because it removes them, and the path is lost. Expecting folks to notice the auto-deleted close-duped questions, manually resurrect them, and then vote them into positivity — as was for that very reason done here, is just too much work, and most such questions will be missed.