This is closely related to an old question on Handling “look at this link” type of answers, which focussed on what the community's response towards such link-only answers should be, and is technically answered by the SE policy in the How To Answer guide:
Provide context for links
Links to external resources are encouraged, but please add context around the link so your fellow users will have some idea what it is and why it’s there. Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline.
In many cases low-quality "answers" which include little more than a bare link would make a perfectly good comment, but a poor answer. The susceptibility to link rot is a genuine concern - more so now that CV has got older, and its effects are starting to set in! So the policy seems very sensible to me, and my question is more about how, as an end user, I should take regard of it when I encounter such an answer on the site.
Downvoting a relevant and helpful link seems harsh - particularly to a new user unable to post comments for technical reasons. But it would presumably be the most appropriate response if this was felt to be an "answer quality" matter to be resolved by voting. If on the other hand we treat such "answers" as suffering a fundamental functional problem, then some sort of rectification is preferable.
One possibility is editing the answer to include more context, so it is no longer just a link. But this is something that the original answerer is usually better placed to do. Another option is to convert the answer to a comment, which would be its more natural place - but that is something for Moderators. If this is the preferred response, presumably regular users should use the "not an answer" flag to bring this to their attention? In the review queue, there is also an option for "recommend deletion" (I believe high-rep users have this tool even outside the review queue). But completely removing a relevant link also seems unsatisfactory, for obvious reasons. Are these deletion recommendations sent to a queue which is checked manually by Moderators, who could convert to comment instead?
It seems to me that most of the time, if we encounter such an "answer", the appropriate response would be to flag it - at least, if we did not have time or knowledge to edit in the contextual information necessary to render it a self-contained answer, or thought that the link was so extraneous that it was not even worth saving as a comment. Is this a fair summary of the situation?