sendoff vs so long

sendoff

noun
  • A party for a person (i.e. a fellow employee) who is leaving; a farewell party. 

  • A party to recognize the passing (death) of a friend and allow survivors to reminisce about the person's life. 

so long

intj
  • Goodbye; a valediction used when leaving or departing from a person or place. 

How often have the words sendoff and so long occurred in a corpus of books? (source: Google Ngram Viewer )