Q:

Can a close vote be taken back?

I voted to close a question as "not a real question". It has since been revised and improved. Is it possible to "take back the vote"?

A:

It's not possible: Once you vote for closing, you cannot change the closing reason, or take it back. Not even moderators can remove a vote. It would be possible, for a moderator, to close the question, and re-open it; I don't see any reason for doing this, as other users should not blindly vote to close because somebody has already voted to close a question.
What you can do, if you voted to close as duplicate, is to remove the automatic comment Stack Exchange adds when the first user vote to close, and eventually add a comment saying that you were wrong.
With "not a real question," there isn't much to do; you could add a comment saying that the question is not acceptable, but that is probably non necessary, as users should first check if the vote to close still applies, before to vote. Considering that there should be 5 users to close a question, it is rather probable the question will not be closed.
Closing votes expires, later or soon; when this happens depends from the number of times the question has been seen. It means that, at some point, nobody will see your vote to close the question.  

