Update: This has been implemented according to the slightly more aggressive manner proposed in this answer below.
Since I don't have 10k here on MSO, I can't really tell when or why those questions were deleted, but I assume there were valid reasons for it. However, regardless of the reasons for the deletion, having the questions that were closed as duplicates of the deleted question remain closed seems like a disservice to users.
Presumably, a duplicate of a deleted question either:
is no longer a duplicate, and should therefore be reopened; or
is crap, just like the deleted question, and should therefore also be deleted.
I therefore propose that, when a question is deleted, any other questions closed as duplicates of it should be automatically flagged for reopening and/or deletion.
I'll leave the exact implementation details for the devs to decide, but one option might be to just add the dupes to both the reopen and the deletion queue, and let the reviewers in those queues decide their fate.
Or perhaps the 10k auto-flag system used e.g. for "questions closed without comment" could be adapted for this purpose too.
Edit: I like animuson's suggestion of automatically adding dupes of deleted questions to the reopen review queue, but with the "leave closed" button replaced with "delete" / "recommend deletion" (since just leaving the question closed is not really a useful option in this situation).