I just came across this question, and it made me wonder what the policy is for deleting questions which have duplicates pointing to them. I don't have any particular stake in this specific question, but it seems like a poor state of affairs for the reader when a question is closed as duplicate, yet the original question does not exist. Should the duplicate question be reopened? Should the original question be undeleted? In this case, the question seems to be a fairly poor-quality question, and "for reasons of moderation" suggests that the original is too, so perhaps this should be marked as a duplicate of a different question?
Since end of January 2015, duplicate targets cannot be deleted anymore (not even by moderators). Before such a question can be deleted, its duplicates have to be either reopened (and possibly reclosed as a duplicate of another question or for other reasons) or deleted first.