I wouldn't worry too much about this crippling global internet traffic. After reading this I looked at a geographic "internet map" and from the looks of things, the only countries (other than the US) that might be seriously affected by the use of such a kill switch would be Mexico and Canada (Canada in particular). It looks like a lot of their internet traffic is routed through the US rather than going directly to its destination, and while Mexico has independent connections to South and Central America, Canada doesn't appear to have many independent connections to other countries.
The US and Europe are heavily interconnected and each appears to serve as a hub of sorts for more remote countries. Fortunately there don't seem to be many places whose only means of communicating with the outside world is via the US (most connections are redundant and multiple paths are available). Most smaller networks connect to both US and European networks (Europe is depicted as such a dense blob of connections that an individual country's networks are hard to discern, although Germany appears especially well connected), as well as major hubs in Indonesia, India and Japan. Thus, even the worst case scenario wouldn't bring the global internet to a halt, but it may slow down communications, particularly for the more isolated networks. That being said, the US does hold the largest single piece of the internet, and it would put the Department of Homeland Security in a position to do about as much harm as it is possible for one agency to do (which fortunately isn't much).
Another thing to keep in mind is that the "kill switch" analogy isn't very apt, as an ISP can be ordered to do a number of things besides shutting down, such as blocking traffic from individual countries. This would mean that if this power were used as intended (and that's a big if) most of the world probably wouldn't even notice. The thing I find the most troubling about this law is that it would give the US government the ability to shut down internal communications (including telephone access) at will, which could be a powerful tool in the hands of a despot.
On another note, if they're worried about an attack on infrastructure, like the electrical grid, wouldn't it be simpler to require utility companies to keep their critical systems isolated from the internet? Some utilities like sewage treatment plants are essentially self contained and shouldn't need to communicate with outside networks in the first place. Electrical distributors do need to share data, but they already have a network of electrical transmission cables which can be made to serve double duty as data transmission lines (the practice is known as powerline networking). It shouldn't be that difficult to create their own isolated communication network which has, by virtue of being transmitted over the electrical grid itself, every connection they should need to make with another electrical company.