It's a scary thought to me that 90% of online videos are hosted on YouTube. If Google were to ever fail, I know that won't happen, but I think the internet would be truly broken if for any reason YouTube is down.
I can't honestly say youtube disappearing won't have an impact, but it will not be the end of the world even I won't get to archive all the items I want. Something will replace it. And if it doesn't, that is ok too.
Imagine the falloff of internet traffic.