Although the idea of switching off the root servers, or removing all entries for non-screened sites would be quite effective, I think you can make
some preperations now. It's no silver bullet but it may well be a way around it at first.
There are alternative root server systems such as OpenNIC:
There are also alternative DNS servers such as OpenDNS:
If you start researching these alternatives, you will find many of them. All you have to do, is learn how to make your computer use a different DNS
system (It's explained on their webpages), and store the IP addresses of their servers somewhere safe.
Any killswitch may be even more powerful, it may just shut down all consumer connections at the ISP level. One possible way around that may be to use
a very small, local ISP. Often the rules don't quite apply the same to those very small ISPs, I believe they don't have to have monitoring rooms or
black boxes installed.
Of course these things aren't foolproof, but the more knowledge people have, the more chance of being able to gain access if the SHTF.
I expect in any serious SHTF situation, or local fascism, there will still be tech gurus quietly telling their friends/family how to get around any
such systems, in the same way we saw when Iran cut a lot of the internet during the recent election.
I find it difficult to believe they could really shut everything down without people going crazy, I expect that they'd do more like limiting speeds,
limiting what sites you can go on, stuff like that, so the regular drones can still get their X-Factor fix, but people coming to sites like this, or
others to organise will be locked out.