Blockr.io has been discontinued by Coinbase and now all links pointing to this explorer redirect to Coinbase.com. Should we edit past questions and answer that used this explorer to point to another one?
Generally, dead links should be fixed where it is easy to do so. If it cannot be fixed, the link should be removed. If the question becomes obsolete without the link, it should be removed (e.g. via being flagged as "very low quality" or "not an answer").
If you have the time to do so, the replacing of the broken links would be appreciated, but I'm not sure if it's important enough for anyone to manually work through all of them.