"Departed" is a polite way to say dead, but it is also frequently used to mean "left the area," as in "The bus departed at ten thirty this morning. It is gone."
"passed away" is also a polite way to say dead. I would say this is probably the most commonly used polite term, in America, at least.
"perished" is usually only used in by news reporters. "Three people perished in the fire."
"death" is a noun form of "dead."