Suppose I put up a question which I think contains some flaw. If the question is proved to contain a flaw by others, thus making it unanswerable, should I delete the question, or should I let it stay?
If the question has an upvoted answer, the issue is moot: you will not be able to delete it. Generally, you should refrain from deleting questions with a 0-score answer too (unless the answer is also worthless).
For unanswered questions, a guiding principle can be: what will make The Internet a better place: the existence of your question with a comment indicating it is unanswerable, or its absence? There is a spectrum between "a natural, naive question with an insightful comment" and "esoteric question that will be a dead-end in search results for users looking for something else". So, consider how natural the question is, and in what sense it is "unanswerable". At the end of the day, it's your call.