Recently I came across a question from a user that was a clear abstract duplicate of a previous question they'd asked (the two were related by trivial algebraic manipulations). I voted to close the duplicate question, but the duplicate rather swiftly rolled off the front page and 'into the mists'; it doesn't seem to have attracted any other close votes (or comments disagreeing with the one in place). Is it appropriate to also flag the question for attention/opinions from others, or should I just let it be?
If you vote to close a question, it will automatically enter the Close Votes review queue.
There, it will get attention from people who can vote to close (>3k rep, off the top of my head).
Hence, there is no need to draw extra attention to the question. It should resolve itself.