Depends - It doesn't help if the DNS server is dead, but the front-end is still advertising the routes.
It came back to life for me a few moments ago (via Cogent) and it looks like the routing did not change (there is a bunch of 10/8 stuff in the traceroute).
Looks like it's back here. However, they clearly have more problems. At the moment, the two name servers that the youtube.com domain is delegated to, dns1.sjl.youtube.com. 1H IN A 208.65.152.201 dns2.sjl.youtube.com. 1H IN A 208.65.152.137 reply ok. However, they reply that the youtube.com domain is served by youtube.com. 1H IN NS dns1.sjl.youtube.com. youtube.com. 1H IN NS dns2.sjl.youtube.com. youtube.com. 1H IN NS dns3.sjl.youtube.com. youtube.com. 1H IN NS sjl-ins2.sjl.youtube.com. but reply with NXDOMAIN when asked for the A of sjl-ins2.sjl.youtube.com. Steinar Haug, Nethelp consulting, sthaug@nethelp.no