It was very thoughtful of the Buddha to die.
After all, he taught the inevitability of change, impermanence, death. If he'd somehow found a way to avoid death, it would have been discouraging and a bit confusing for the rest of us.
But, in the end, isn't that what he did? Wasn't his entering Nirvana the end of birth and death for him?
From that point of view, his no longer dying is one of the most inspiring feats in history.
"Everything is changeable, everything appears and disappears; there is no blissful peace until one passes beyond the agony of life and death."
"Beyond the agony of life and death." Sounds like a nice place, from here!
Another interesting teaching of the Buddha's on death was when he asked a group of monks;
"How often do you contemplate death?"
One of them replied, "Lord, I contemplate death every day."
"Not good enough," the Buddha said, and asked another monk, who replied,
"Lord, I contemplate death with each mouthful that I eat during the meal."
"Better, but not good enough," said the Buddha, "What about you?"
The third monk said, "Lord, I contemplate death with each inhalation and each exhalation."
He explained that contemplating death relieves fear, encourages us to live with proper values, and lets us to die a good death with fortitude and calm. I think, basically, get used to the undeniable fact that you must die.
It would be a fair question for one to ask, did the Buddha live up to his words?
According to the Mahaparinibbana Sutta, it was like this;
1. Then the Blessed One spoke to the Venerable Ananda, "It may be, Ananda, that to some among you the thought will come: 'Here we have the words of the teacher who is gone; our teacher we have with us no more.' But it should not, Ananda, be considered in this light. For that which I have taught and made known as the Dhamma and the Discipline, this shall be your teacher when I am gone.
2. "And, Ananda, whereas now the bhikkhus address one another as 'friend,' let it not be so when I am gone. The senior bhikkhus, Ananda, may address the junior ones by their name, their family name, or as 'friend'; but the junior bhikkhus should address the senior ones as 'venerable sir' or 'your reverence.'
3. "If it is desired, Ananda, the Sangha may, when I am gone, abolish the lesser and minor rules.
4. "Ananda, when I am gone, let the highest penalty be imposed upon the Bhikkhu Channa."
"But what, Lord, is the higher penalty?"
"The bhikkhu Channa, Ananda, may say what he will, but the bhikkhus should neither advise him, nor exhort him, nor admonish him."
5. Then the Blessed One addressed the bhikkhus, saying: "It may be, bhikkhus, that one of you is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. Then question, bhikkhus! Do not reproach yourselves afterwards with the thought: 'Our teacher was with us face to face, yet face to face we failed to ask him.'"
6. But when this was said, the bhikkhus were silent. And yet a second and a third time the Blessed One said to them: "It may be, bhikkhus, that one of you is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. Then question, bhikkhus! Do not be given to remorse later on with the thought: 'The Master was with us face to face, yet face to face we failed to ask him.'"
And for a second and a third time the bhikkhus were silent. Then the Blessed One said to them: "It may be, bhikkhus, out of respect for the teacher that you ask no questions. Then, bhikkhus, let friend communicate it to friend." Yet still the bhikkhus were silent.
7. And the Venerable Ananda spoke to the Blessed One, saying: "Marvellous it is, O Lord, most wonderful it is! This faith I have in the community of bhikkhus, that not even one bhikkhu is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice."
"Out of faith, Ananda, you speak thus. But here, Ananda, the Tathagata knows for certain that among this community of bhikkhus there is not even one bhikkhu who is in doubt or perplexity as to the Buddha, the Dhamma, or the Sangha, the path or the practice. For, Ananda, among these five hundred bhikkhus even the lowest is a stream-enterer, secure from downfall, assured, and bound for enlightenment."
8. And the Blessed One addressed the bhikkhus, saying: "Behold now, bhikkhus, I exhort you: All compounded things are subject to vanish. Strive with earnestness!"
This was the last word of the Tathagata.
Already freed from his own dukkha, the Buddha was able to devote his last moments to easing the suffering of his Sangha. There was surely still a great sadness, but the Buddha made it easy.