A few notes on the previous posts…
Increasing federal power is definitely not “du jour” unless your “jour” is pretty long. Federal power increased dramatically in the 1930s under Franklin Roosevelt as a response to the New Deal. Lately, the present Supreme Court has taken some steps, albeit baby steps, toward returning power to the states. While it is clear that the present allocation of power between the federal government and the states is not that contemplated by the founding fathers, that hasn’t been true for a very long time. In fact, now that I think about it, the first dramatic change in the balance of power resulted from the Civil War, Reconstruction, etc. Given a choice between being divided into 50 separate states (using the term in its political science sense) or 50 parts of a single state, I suspect that most of the founding fathers would prefer a single united country, as evidenced by the federalist papers and the debate over the Articles of Confederation. But that’s just IMHO.
In many instances, state constitutions grant more rights than the federal constitution. For example, some states’ constitutions (I do not recall which states and could probably look it up if anyone really cares) grant greater rights with respect to the 4th Amendment and search and seizure law. In those states, the state police are more restrained than in the states where their equivalent constitutional guarantees have been determined to be equivalent to the federal guarantees.
The basic structure is that the Federal Constitution preserves certain rights nationally, sets out the limited powers of the federal government, and leaves everything else to the states. Where the federal constitution and Congress has not preserved something as a right or legislated against it, it’s up to the states. That’s why some states could allow abortion before Roe v. Wade and some could prohibit it. Of course, once the Court found that the federal constitution preserved the right to an abortion, the matter was taken from the states’ hands.
In response to BobT, the Supreme Court would not be able to narrow state-granted rights, unless they conflicted with existing federal constitutional guarantees or Acts of Congress. The only way state laws or constitutional rights get restricted is through preemption.
Returning to the OP, if the federal constitution were either amended to remove the 2nd Amendment, or it were somehow read out of existence by a Supreme Court decision, then the issue would be up to the states.
Where it becomes sticky is where Congress acts in a way incompatible with the state constitution. I ** think ** (but do not recall for sure) that an Act of Congress would preempt a contrary state constitutional provision. So, if the federal government created a national gun registry, I ** think ** that the federal statute would prevail over a contrary state constitutional provision.