I don't see why not. There's no provision that stops them from first amending out the last sentence of Article V. And more generally, the Supreme Court is the final arbiter of constitutional questions and I don't think they would stand in the way of a document that was ratified by the requisite number of states.
I'm not sure that's the case. Essentially the Constitution represents a contract between the federal government and every state that joins the Union. And one of the terms of that contract is that every state gets equal representation in the Senate. Even if 49 states decided that New Jersey should no longer get two Senators (which is reasonable), New Jersey would still need to agree to this loss of representation.
Completely abolishing the Constitution, I would think, would require the consent of every state.
But the sentence that says no state shall be deprived of equal representation in the Senate without its consent is amendable by the normal amendment process. The Founders could have put a clause at the end of Article V saying that nothing in Article V could be amended, entrenching the amendment process and equal representation in the Senate irrevocably. But they didn't.
