This is somewhat related to an older question regarding link rot, where one of the courses of action was flagging for moderator attention.
When it comes to link rot, all I can do is leave a comment to the author and hope they (1) visit the site to receive it and (2) find a replacement link. At that point, there's not much else I can do but dismiss the flag as helpful, provided the answer still makes sense despite link rot.
Answers that are just one link and can't stand on their own if that link breaks should just be removed.
Answers that stand on their own even with a broken link, especially if highly up-voted or accepted, should be saved. We do have ten moderators and at least one of them has the generalist badge, but it could take days before all ten of us look at a flagged post. Putting these in front of thousands of people an hour vs ten a week seems like a better idea.
Would it be possible to add a "broken link" flag reason that stays in the 10k+ queue (which I hope will shortly open up to all S&W recipients), eventually trickling into the moderator queue if left unfixed?
Broken Link: This answer is of acceptable quality, but lost some of its value due to a broken hyperlink. A replacement link should be found. If this answer makes absolutely no sense due to the link being broken, it should be flagged as Not An Answer
Not An Answer: This was posted as an answer, but it does not answer the question. It should possibly be an edit, a comment, another question, or deleted altogether.
... or something like that.