I believe that this should be determined on a case by case basis by considering what would be the most useful to future readers of the site.
If the question is on topic, I don't see the benefit of editing it to make it off-topic. I've seen the reverse encouraged here "it may be necessary to reword the question to fit this site's scope after reviewing the community guidelines." but have yet to see anything to indicate that a post should be edited to make it off topic.
