What I'd suggest is to link to the video and also include a quick text/image summary of whatever the crucial part of the video is, like a couple of quick bullet points, and/or an image and a line or text saying what's happening.
- The answer still has value if the video goes down
- It helps people understand what your answer is about faster. Some people (including me) get a bit grumpy and impatient trying to wade through a video past lots of stuff they already know for the crucial bit that contains the new or unusual trick.
- People who like watching the whole video still can, and benefit by knowing what part they need to pay extra attention on.
So for the example you linked to, you'd link to the video, say that it's the Shape builder tool that is shown, show a snipped screenshot from, say, 0:45 which shows the key basics people could get started with...
...then just say that after applying the shape builder tool you can click, drag etc etc and it switches between different intersections of the shapes.
While the video is still there, you're giving people an idea of what they're getting and helping people get straight to the important part. If the video goes down, there's just enough that people can muddle through without it.
On Windows, you can get screenshot snippets with the Snipping Tool from the Start menu under
All Programs > Accessories. On Mac, it's
command + shift + f4.
I'm no lawyer but I'd be amazed if one partial screenshot linking back to the original wouldn't always be considered "fair use".