It's not as simple as "the Internet goes down", I regret that headline in some ways. I really see two major things that can happen:
-Individual sites find their traffic capacity exceeded - a lot like what happens in a DoS attack, but just from natural demand. Even the biggest websites will have difficulty processing requests from a majority of Internet users in the world at once. You'll note from the article that even Google News experienced serious service trouble from this, and it may be safe to say Google has more outright traffic capacity than anyone in the world (unsure, but up there in terms of probability). Their webservers will either be clogged or crash outright, and then you have a chain reaction effect - if one popular news site (CNN) goes down, the users will go to, say, MSNBC, Time, or Newsweek, and then each of those sites is under a greater load and possibility of going down. With enough demand in a particular area - e.g., Jackson's death - you could get sort of "localized cascades" that leave the majority of sites unaffected but shut down major sites in key sectors.
-Mid-level routers crash or become clogged. Again, it just depends on demand, but you can get the same kind of chaining effect if the spike is big enough. The more backup equipment you have, the better chance you have that they can take a load that heavy. But if things start going down, then other servers are going to try to reroute through other paths, since really it's all just a big web (I don't even want to think about how hard it must be to program the software for top-level DNS servers).
Jackson's death seems to have primarily caused the first. That could be a sort of stress test for the Internet - I mean, really, this IS the most practical stress test the Net has had so far - in terms of diagnosing that individual sites are likely to be the biggest bottlenecks and the most vulnerable in a demand surge, not routers or the actual "inter" part of the internet.
There is the possibility that a major backbone DNS server goes down, or that there's a problem with the big, major cables that connect some of the fatter and longer physical pipes out there. I see that, though, as more likely to be caused by physical damage to either the site server location or the lines bringing it around the world. Lightning, tornado, earthquake, explosion and etc. Damage to the undersea cables that link countries together seems to me like a distinct risk that somebody must be trying to deal with:
http://en.wikipedia.org/wiki/Submarine_ ... ions_cable
(TBH, by the way, as a postscript, submarine comm cables blow my mind, period. The notion that we can lay a cable capable of carrying anything important OVER AN ENTIRE ____ING OCEAN is mindblowing to me. Not only that - but the fact that the world has had them for a hundred and fifty years. Here's a crazy-ass picture of what intercontinental telegraph cables looked like in frickin' 1901:
http://en.wikipedia.org/wiki/File:1901_ ... cables.png)