Business would come to a stop. How do businesses interact with suppliers and customers these days? How do banks interact with each other?
Years ago, businesses would maintain leased lines. These days, it's increasingly encrypted connections over the Internet.
I can see the feds deciding that certain web sites will be kicked off from Internet connectivity, but they can't shut down the whole net. So, instead of Doomesday scenarios, consider how we would recreate FR quickly if a federal agency just issues a series of edicts to ISPs to shut off a whole bunch of conservative sites.
We could name it "NotSoFreeRepublic.com".
“Has anybody really considered what would really happen if the entire Internet shut down?”
I don’t think Hussein would ever shut down the “entire Internet”; it’ll be cherry-picked and only certain people and groups will be impacted. We should plan on being one of those groups.
I agree that it would be a more targeted approach, to preserve the government's own comms, in part.
Sites like this will get clobbered, but an e-mail list server which copies any registrant's message to all hands - that might not be at the top of the list to shut down. Particularly if it has an innocuous name.
Keep in mind, too, that P2P sites - especially those not on U.S. soil - could be useful. Back in Napster's heyday, I downloaded what I thought was an .mp3 file of some old radio show. It was actually a zip file of documents from the Stormfront white power types. The trick is to disguise the file as something that only certain people would go looking for, and using some sort of identifier in the file name - like a strategic typographical "error".