No Constitutional method?
There’s nothing stating they CAN’T. They may, as per the Declaration, dissolve the bonds, as needed/necessary.
The majority will does not compel the minority in ANY way.
The whole point of the Constitution was to create a more perfect, “perpetual” union. Argue with Madison, not me. Once a state was in that union the only certain means of leaving would be a constitutional amendment
Even the Slavers knew that, and that it would never get out constitutionally so they held an insurrection better named “the RAT Rebellion”.