I don't know what happens to "closed" questions. If they disappear from search results, and the answer is something that can be used again for other people, then they shouldn't be closed (IMHO).
I do close questions that are not useful to others. For example, I recently closed a question requesting that two PPPs needed to be merged, but they were locked. Someone came along, unlocked and completed the merge. That type of question is not something that necessarily needs to stick around.
Now, if the question had been something like "What do we do when two duplicates are both protected?" then I would have not closed it.