I don't think that the fed will shut down the Internet. Not just because it's effectively impossible to do for a timeframe that's anything less than a month, but because it would literally destroy the entire country and the regime's ability to do anything.
There's a reason China still has the Internet, and why VPNs are still kind of tolerated. The U.S. nor any industry in it cannot survive without it. We are dozens of much less serious (but still serious) steps away from an internet shutdown, and I genuinely think that we won't reach internet shutdown at all.
Without the Internet it's not just credit cards that stop working, it's literally the capability for any store to order stuff to sell. Or the capability for every federally regulated employer (nearly all of them) to pay employees. Third world countries can get away with it because their economy isn't anywhere near as modernized as that of western countries.
Additionally, the way that the U.S. government is organized makes attacks on the Internet very difficult without Congress.