[abustamam]

I'm not sure why you're singling out YouTube here. YouTube is the main go to place for videos on the web, so it shouldn't be surprising that most of the videos posted here are hosted by YouTube.

Concerning, maybe, but the same could be said of a lot of other centralized mediums (such as Medium, WordPress, even HN threads itself).

When you rely on someone else to host your stuff, you always run the risk of it disappearing. Important stuff should always be backed up, whether it's video stored on YouTube or an amazing blog post on medium.

If YouTube disappeared tomorrow and all these videos disappeared, I'm sure within a week or month, people will have reuploaded many of the really great talks posted in this thread on some other site.