I found a similar question on Meta StackExchange asking What exactly happens with the button “Leave Open” (previously “Do Not Close”)?
The accepted answer to that question states the following (Emphasis mine):
Normally, a question must hit 100 views before close votes age away, so as to give enough folks time to see and review it. Questions with close votes stay in the review queue until they are closed or the votes expire.
But if enough people (currently 3) select "Do Not Close" within the review queue, the question will be immediately removed from the queue (not shown to any more reviewers) and the aging starts immediately.
This doesn't prevent it from being closed, mind you - if someone visits the question directly and votes to close it, that'll both count toward the 5 votes needed to close it and stall the aging for another four days - but it will both reduce the number of people viewing it and hasten the removal of votes on questions for which there is clearly no support for closing.
This means that using the "Leave Open" button does not remove the existing "Close" Votes. It's just that if enough people vote to "Leave Open" the question is removed from the Review Queue so as to not get as much attention as before. If people visit the question and think it should be closed it can still be closed.
The "Leave Open" Votes do not have a direct impact on the "Close" Votes. They have an impact on the visibility of the Voting process and on the "aging away" process.
You need 5 "Close" Votes to close a question and the "Close" Votes start to age away at a certain point. The aging starts after 4 days have passed since the last "Close" Vote has been cast and the question has at least 100 views, unless there have been enough "Leave Open" Votes. See here for reference.