I think this is a no brainer. As biophase noted, hardware necessary for disk space and bandwidth is getting cheaper. In fact, from what I'm seeing it is digital technology of all things the prices of which just keep getting down and down while the quality and quantity goes up. It's incredible. I've read several articles which reveal why is it so easy nowadays for companies, not even biggest companies, to provide huge bandwidth and hosting space. It's practically abundant.

And 80 million a year on those few ads that show is a pretty nice deal. If they need more they can just add a little more ads (albeit not too much as that could have a backslash in terms of users jumping ship to other sites).

I think you just have nothing to worry about. Even if it somehow magically happened that YouTube went down there is a number of alternatives. Just keep an archive of all your videos offline backed up somewhere and you can just switch to a different site (like metacafe, dailymotion etc.) in a matter of a day.

Cheers