What happens when the internet vanishes?

I honestly can't be sure the internet ever will "vanish". It can drastically change and definitely has from it's birth, but as long as there is networking equipment and nerds there will always be an internet.

The mechanics of doing so in the US would make it very hard to pull off and getting it to stand up in the courts would take a completely corrupt SC.
Huge sections of industry shut down as retail; many stores do shortly there after, Security systems and burglar alarms fail.

Chaos. Utter chaos.