Does this mean that achieving Nirvana is not the final goal for Mahayana and Vajrayana Buddhists but achieving 'full enlightenment' is?
According to Mahayana teachings, even Hinayanists will eventually hear the thunderous sound of the drums of the Heaven of the Thirty-Three, awakening them to the need of achieving full enlightenment for the sake of all mother sentient beings.
In this sense, Hinayana and Mahayana merge into ”Ekayana”, or ”One Vehicle”.
Because only when we are the Fully Enlightened Buddha (Samyak SamBuddha) then we are able to fulfill the wish for saving all sentient beings as we will be obtaining the rupakayas as well?
Sure. However, Hinayanists do have the wish to save all sentient beings as well, which is their infinite love and compassion, but they believe that, except for the rare bodhisattva, they themselves and other sentient beings can at best become arhats, and that the only way to help all sentient beings to become arhats is becoming arhats themselves; therefore, they become arhats and enter nirvana for the sake of all sentient beings. Therefore, even Hinayanists are wonderfully altruistic.
Still, Mahayanists understand that their happiness will never be complete if they merely become arhats in nirvana, incapable of further and ceaselessly helping all mother sentient beings until samsara is empty, and therefore generate great love and compassion for all sentient beings, like a mother for her only child, and then bodhichitta, or the wish and then the vow to attain a buddhahood endowed with a dharmakaya and a rupakaya, so that all mother sentient beings may also achieve exactly the same state, after themselves, together with themselves, or even before themselves, as exemplified by Buddha Shakyamuni, Maitreya, and Manjushri.