The economic impacts of this - both national and global - would be utterly catastrophic, almost beyond imagination.
To begin with, I'm going to guess something like 25,000,000 people in that area; if you start out assuming 14,000,000 dead, that leaves 10 million displaced - and where are they going to go? Who's going to pay to relocate them? Remember, the vast majority of the survivors will have lost not only their jobs but everything they own. Tens of millions of people will be unemployed in a very short time - not just the residents of that area, whose jobs, businesses, and farms will all be underwater, but perhaps as many as tens of millions of people all across the country who work in industries dependent on that region. Hundreds of trillions of dollars worth of commercial, residential, and agricultural property is just wiped completely off the books, and considering how many average Americans have almost all of their lifetime net worth stored in their home equity, that means that tens of millions of people are basically bankrupt and have to start over in a strange place.
Almost all of the nation's wheat and corn production is gone, along with much (or most) pork and beef. From eyeballing that map, I'm gonna guess maybe 60% of the country's crude oil production and refining capacity, maybe 45% of the natural gas. A lot of that production will eventually be recoverable by deep sea drilling, but it would take years to get up to speed, and the refineries would have to just start from scratch. We'll have to import most of our oil, but the ports that can handle petroleum imports are all underwater.
Think back to Hurricane Katrina, in 2005. Basically one large metropolitan/industrial area flooded, and it knocked an estimated 1.1% off our GDP. Can you imagine he effect on the GDP if you multiply that by hundreds, or even thousands? This isn't just a matter of redrawing some maps and relocating some people; this is something that would actually be comparable to the eruption of the Yellowstone super-volcano. It would be unprecedented in recorded human history.
Add to that the human costs that result from such widespread trauma - depression, suicides, alcoholism, PTSD, broken families, etc. Millions of people will need not just financial and logistical help, but emotional, spiritual, and psychological support. The country would be in a state of shock, for many years to come. Many people will never recover from their losses.
Politically, the country is in chaos. The majority of the people will be deeply unhappy with the way the government handles the crisis, no matter that they do. All of the states that have been evacuated are Red states, and the majority of the refugees will be conservatives moving to states that are mostly Blue. Internal politics of many of the remaining states will bein turmoil as new residents demand financial assistance that many of the states will not be able to afford, because they're all going to be badly damaged by the Depression. Blaming, vilifying, and angry fingerpointing will be the new norm in a country still deeply inflamed by the Vietnam War divisions.
The US is basically knocked back to almost a 3rd world economy, heavily dependent on food and fuel imports from countries who suddenly don't really need us as much as they did when we were the biggest kid on the block. Other major powers such as Russia and China will be able to cut more favorable deals for commodities, pricing us out of the market and forcing us to deal on their terms. Aside from our nuclear arsenal, we would quickly become a middle-of-the pack military power, because we won't even be able to afford to feed our own people and keep our lights on. The era of projecting unlimited force anywhere on the planet to achieve our national policy objectives are over; we can't afford that anymore. Our internal problems will take priority. For many years to come, we are basically post-WWII Europe.
As far as international affairs are concerned it's now the Soviet Union's world, and there won't be a damned thing we can do about whatever they decide to do. The Cold War will come down to a world-wide pissing match between China and Russia, and the nations of Europe, Africa, the Middle East, and the Western Pacific will have to choose sides between the two of them and line up in whatever way they feel suits their best interests. They won't be getting any more help from us for the foreseeable future. Both countries will be in a good position to achieve their goals through diplomacy, because the US is just no longer a player - who else is everyone gonna deal with, but the Soviets and the Chinese? Longterm, China will emerge as the world's sole superpower, because the inherent structural flaws in Soviet society are irreparable, and the collapse of their house of cards is inevitable at some point. In the short term both Russia and China will jockey for position in Central and probably South America, trying to turn those poorer countries against their imperialist neighbors to the north.
And, finally - the Dallas Cowboys never become "America's Team", and disco never really happens because people won't be able to afford cocaine. So, it's not entirely bad after all.