run its course vs slip away

run its course

verb
  • To come to a natural end. 

slip away

verb
  • To disappear; to elude one; to recede; to dwindle. 

  • To leave a place, or a gathering, without being noticed. 

  • To die peacefully. 

  • To pass quickly, almost unnoticed. 

How often have the words run its course and slip away occurred in a corpus of books? (source: Google Ngram Viewer )