Um, no. How on earth would the price of oil at home become 'decoupled'? What is there to prevent the oil companies from charging the same price as the rest of the world? It's a free country after all! And it isn't like the government could force them to sell at a set price, because we are...a free country. Unless you want to impose price controls, which is stepping pretty far into socialist territory and probably illegal.
Seriously, I have no idea how any of what you suggest would work in the real world.
I foresee something different. In the event of a game changing event: the historical precedent is the crude oil export ban which was law from 1975 to 2015, in other words, I am discussing import / export controls, not price controls. If the Gulf shuts down, you would see this law reinstated. As North America has enough hydrocarbons to be self-sufficient, you would see a bifurcated market with prices for North America and prices for the rest of the world.
For example (using ballpark numbers), world oil consumption and world production is 100M BPD. North America consumption and production is 20M BPD. The Gulf shuts down, 20M BPD comes off the market and prices skyrocket - gas goes to $8-$10 per gallon. If what you are saying is correct, the American political system does nothing. What I am saying is that the historical precedent from the Arab Oil Embargo of the 1970's is that Congress makes it illegal to ship oil abroad - all crude must be used domestically. The difference between 1975 and now is that we have the capability to produce enough crude to not need imports.
You now have a situation where North America is still at the same 20M BPD - it just stays within the Western Hemisphere. Exxon, Chevron, BP, Anadarko, Devon, Chesapeake, etc - there are more than enough oil companies pumping to provide price competition and although it could possible rise somewhat, the nature of shale production is that it can be turned on very fast. The bigger problems might be financing and/or refinery capacity matching up the different grades of crude.
That said, the rest of the world will have a problem. You now have every other country bidding for the remaining 60M BPD and prices will skyrocket. The interesting thing is that if we are paying $70 per barrel for transportation and raw materials and the remainder of the world is paying $170 per barrel, we have a competitive advantage.