i don't think passed away is a new saying - intruigued me so I looked it up
"pass away
Also, pass on or over . Die, as in He passed away last week, or After Grandma passes on we'll sell the land, or I hear he's about to pass over. All these terms are euphemisms for dying, although the verb pass alone as well as pass away have been used in the sense of "pass out of existence, die" since the 1300s. The two variants-adding on [c. 1800] and over [c. 1900]-allude to moving to some other-worldly realm"