Broken links don't provide any useful information. And contrary to what the author of that questions claims, they don't prove anything either, because nobody knows if that link ever existed. After all I could claim that the NY Times posted an article which says that Jeff Atwood eats babies which they then removed without a trace because the secret world government told them to*.
So there is no reason to intentionally keep broken links.
However, what's even better than removing the link is to fix it. If you feel diligent, you could try to find out if the document was moved to a different URL. You could also see if there is an archived version of the document on the wayback machine of archive.org and link to that. Which happens to exist in this case. I updated the question.
*) Although in the case of the article in the linked question, it seems it was apparently depublished because the article was bought from Associated Press and the NYT only had a time-limited license to publish it.