The usual philosophy on Stack Exchange is to write answers in a way that is still understandable if a link goes bad. For links to text-based content, this means quote the important part, write a short summary et c. For linked/embedded video, I would say the best way to make a post future-proof is to describe the relevant part of the video, e.g. the effect the poster is refering to, the particular camera angle the asker wants to know more about and so on. The problem is that it's sometimes hard to put that into words, which is why many posters would rather embed a video and mention the timecode of the relevant part. So it just comes down to whether the poster is willing to put in the extra effort.
To add to text-based explanations, screenshots and/or animated gifs could go a long way to preserve the post's validity even if the video goes offline at some point. Of course, those shouldn't be hosted on servers that are likely to shut down at some point, but if we use the upload tool that uploads to
stack.imgur.com it's as future-proof as we can get without archiving the actual video.