go missing vs slip away

go missing

verb
  • To disappear without explanation; to become lost. 

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 go missing and slip away occurred in a corpus of books? (source: Google Ngram Viewer )