No, the vast majority of videos on YouTube are not at a particular risk of deletion. Specific topics are, but the average Linus tech tips video is not.

Amusingly, Linus Tech Tips has had many videos censored and removed by YouTube.

I think it’s pretty obvious when they’re gonna get removed. Almost certainly someone has a local mirror of that channel.

it is not at all obvious when some automated check somewhere will flag or remove a youtube video.

all YT videos are in danger of deletion. You can argue whether or not they're worthy of the merit of saving, but you cannot deny their risk for sudden removal.

Archive.org have stated they do not want to be a complete mirror of YouTube which is fair enough. Content creators could easily retain a local copy of files and upload them to archive.org in the even of removal, or an individual could retain local mirrors of channels to do the same thing. Archive.org are aware of the fact that things hosted on websites might disappear, I can’t speak for why YouTube is not a desirable thing to mirror but I assume the volume would be massive and the risks of potential copywrite / illegal / highly illegal content etc would be undesirable from a management perspective.

Yes. Everything on internet can be deleted and modified at someone's will.