Now, whether we accept a traditional interpretation of rebirth or not, having a practice to return to once we know that we're about to kick the bucket sure sounds like a good idea. Obviously, when that time comes we won't necessarily know for sure that we'll be able to physically sit Zazen.
Anyway, here's one of my all time favourite quotes from Master Huang-Po regarding that topic (which in essence sounds to me a whole lot like the Tibetan Book of the Dead without the cultural baggage):
"If an ordinary man, when he is about to die, could only see the five elements of consciousness as void; the four physical elements as not constituting an 'I'; the real Mind as formless and neither coming nor going; his nature as something neither commencing at his birth nor perishing at his death, but as whole and motionless in its very depths; his Mind and environmental objects as one - if he could really accomplish this, he would receive Enlightenment in a flash. He would no longer be entangled by the Triple World; he would be a World-Transcendor. He would be without even the faintest tendency towards rebirth. If he should behold the glorious sight of all the Buddhas coming to welcome him, surrounded by every kind of gorgeous manifestation, he would feel no desire to approach them. If he should behold all sorts of horrific forms surrounding him, he would experience no terror. He would just be himself, oblivious of conceptual thought and one with the Absolute. He would have attained the state of unconditioned being. This, then, is the fundamental principle."