If North Korea gives up Nuclear arms and artillery along the border with S. Korea, then US could remove its 21,000 troops and its THAAD system in South Korea. It can continue having its carrier and cruisers come through the region. China and Russia do not want to see a unified Korea on its border so the agreement would not be unification or close to it and the US could continue alliances with South Korea-- but the border would no longer be a hair trigger artillery range for NK.