To answer the question that is the title, we have to know of what the US consists. Is it an ethnic group, a collection of buildings and resources, a land mass with boundaries, or is it the Constitution. Clearly what differentiates the US from other countries is the US Constitution. The Constitution defines us as a people. Without the Constitution we would be a different country. Therefore, to lose the Constitution is to lose the country.
Does the Constitution still exist? Let us examine the document and come to a conclusion.
The Constitution consists of a description of a republic with three independent branches, legislative, executive, and judicial, each with its own powers, and the Bill of Rights incorporated as constitutional amendments. The Bill of Rights describes the civil liberties of citizens that cannot be violated by the government.
Article I of the Constitution describes legislative powers. Article II describes executive powers, and Article III describes the power of the judiciary. For example, Article I, Section 1 gives all legislative powers to Congress. Article I, Section 8 gives Congress the power to declare war.