the bodhisattva ideal in mahayana / vajrayana is to delay ones own full enlightenment until all beings (not specifically defined) are enlightened. i never asked who the last one would be to close the door behind them when samsara was over though.
It seems that this is not taken literally by some people who have the requisite insight. I think at some point (perhaps in the far future) the goal, for some, is to be re-born and become a Buddha (just like Siddhartha Gotama) and teach the dharma in a realm where it has completely decayed or has not yet existed and re-birth is ended there.
See the below quotes from
http://www.beezone.com/Bodhisattva/bodhisattva.html
From Chogyam Trungpa:Student: You spoke of the vajrayana path as one that could lead to enlightenment in this lifetime. Yet in the bodhisattva vow, we vow not to enter enlightenment until all sentient beings have become enlightened. That seems to present a contradiction.
Trungpa Rinpoche: I don't think so at all. That's the trick of the mahayana path; it helps you to give up. You're not going to attain enlightenment at all; you're going to work with sentient beings. And the idea in vajrayana is that you're going to attain enlightenment in one lifetime. Both work together. In mahayana, the idea that you're not going to attain enlightenment cut your speed, your ambition. In the vajrayana, you develop pride, vajra pride, and dignity. Actually, both amount to the same thing. You can't become buddha in any case at all. Youless, unyou, nonyou, is going to attain enlightenment. That logic holds true all the way along. You can't attain enlightenment. Maybe nonyou can attain enlightenment. Good luck!The Collected Works of Chogyam Trungpa, Vol. 4, p. 191
From Adi Da:The true Bodhisattva is not one who in any sense prevents his or her own Enlightenment in order to first Enlighten others. How can an un-Enlightened being Enlighten anyone else? Rather, the true Bodhisattva is either pursuing ultimate Enlightenment or else he or she is already fully established in the Awakened Wisdom of true Enlightenment while still alive. The Enlightened Bodhisattva is a true Buddha or Transcendental Siddha. And such an individual may intentionally remain in the phenomenal worlds through countless rebirths in order to Awaken others - but this does not involve the prevention of his or her own Enlightenment. The Buddha's or Enlightened Bodhisattvas or Awakened Siddhas that constantly or periodically reappear in the phenomenal worlds for the sake of Helping un-Enlightened beings always reassert their Enlightenment in each lifetime. What they prevent is not Enlightenment but the Hinayana form of Nirvana.