'Pass away' is a euphemism for 'die'.

“去世”是“死”的委婉语。

《牛津词典》

With unutterable misery, the fettered little King heard the voices and footsteps fade away and die out.

戴着脚镣的小国王听到声音和脚步声渐渐消失，直到听不见。真是说不出的痛苦。

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If new neurons are being formed every day in our brain, how can we hold onto these cells and not let them simply die away?

如果大脑中新生神经元每天都在不断形成，那我们怎样才能维持这些细胞，不让它们轻易凋亡呢？

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Talk that Japan's prime minister may call a snap election for parliament's lower house at the same time as the upper-house poll in July will not die away.

ECONOMIST: Japanese politics

The immediate calls for his head from the Tories will now die away and he has certainly won himself a breathing space - but it is only that.

BBC: Byers wins a breathing space

The Giving Pledge, which asks billionaires and near-billionaires to give away a majority of their wealth before they die.

FORBES: Billionaires and their feelings