Many times users simply post an answer to a question which contains a link to an offsite page with little or no context. When that link breaks, what should the policy be to handle those?
Down-vote and comment
Ultimately these answers are bad, but they shouldn't warrant moderator intervention. Instead a comment mentioning the link is broken (as well as mentioning the user should be including the pertinent information) and down-voting will suffice. Enough down-votes will push the answer out of the public space and if the link is only temporarily down the answer will still survive.
Flag for deletion
If the answer can't be salvaged (it's just a link and no replacement can be found and the poster isn't likely to fix it themselves) the post might just want deleting.
If you're doing this, please leave a comment to let the poster know what you're doing - it gives them some additional warning to fix things and makes a moderator's job much easier.
There's a hole in your bucket? Well... Fix it, dear Henry!
There's a hole in the bucket, dear Liza, dear Liza,
There's a hole in the bucket, dear Liza, a hole.
Then fix it, dear Henry, dear Henry, dear Henry,
Then fix it, dear Henry, dear Henry, fix it.
I'd suggest this as a precursor to any voting or commenting. Anybody can suggest an edit so if you see a broken link, Google for an alternative and if you find one, edit the post.
You could even Google for the old URL and try to find the cached version. From there you could look for clues for finding an alternative link and if there's something particularly pertinent on that cached page, and you can't find an alternative, copy in that chunk of the text (within the rules of Fair Use if it's not freely copy-able).
If you can't do any of that, move on to other measures.