die; pass away; visit the Yellow Springs (the underworld)

To search up into the highest heavens and down into the deepest underworld; to leave no stone unturned in an exhaustive search. From a line in the Tang dynasty poem "Song of Everlasting Regret" by Bai Juyi.

(idiom) to return to the Yellow Springs; to meet one's end; to die

(idiom) to harbor regrets into the afterlife; to die with deep resentment or unsatisfied wishes