for keeps vs until the twelfth of never

for keeps

prep
  • With an agreement or intention to retain what one gains or receives. 

  • Permanently, so that one can keep something indefinitely. 

  • With a strong competitive resolve to win or succeed, as in sports or business. 

until the twelfth of never

How often have the words for keeps and until the twelfth of never occurred in a corpus of books? (source: Google Ngram Viewer )