Pass is a keyword in the euphemism of death, both on its own and, more commonly, in pass away and pass on. The first is of considerable antiquity, dating back to the 14th century, the second apparently a comparative 19th-century newcomer, but both encapsulate perfectly the element of sentimental pretence that cannot even come straight out with "go", but has to use the softer, more gradual "pass".
Some questions for consideration:
1) Is this euphemism more common in speech or writing?
2) Is its distribution associated with sociolinguistic variables such as age, sex, social class, education, etc?
3) Are die and pass away really identical in their usage?