Dead links are inevitable if your written content lives long enough online. Include archive links alongside links to off-domain content “(a)”.
I like the idea of including an archive link when linking to off-domain content. It seems like something that I could automate through some “presubmit” step of the publishing process. I’ve looked around but haven’t found an addon/extension for any of the popular blogging solutions which provides an easy way to include such links. I expect that I won’t bother to include them so long as I would have to include them manually. The URL to the off-domain content will be present and determined readers will be able to consult archive.org/etc on their own to achieve the same result.
I also notice that the author includes (sometimes long) relevant quotes from links they cite. I think this is a fantastic practice which accomplishes most of the goal of “(a)”.