日薄西山-----one's days are numbered

例句：
A: How is your very sick grandfiather in hospital?
你那住院且病情严重的祖父怎么样了？
B: Sad to say, his days are numbered.
说来令人伤心，他的生命已日薄西山了。

同义词：
not to be long for this world
The sands are running out.