Why John McCain will not retire from the Senate:

Yesterday  (Wednesday the 20th),  Senator McCain was successfully operated on,  for the removal of a 2 inch tumor attached to his brain.  Doctors believe that small tentacles of this tumor are still in the brain,  necessitating chemo-therapy.  

Apparently the Senator is reasonably healthy in spite of this most recent set-back.  

If his immediate "recovery" allows him to return to the Senate,  I do not expect him to retire.  He is too much of a #NeverTrump politician. His continued presence on the Senate roll-call,  will add to the difficulties for President Trump's agenda and that will be, very much,  to the liking of the Senator.  

McCain is a Status-Quo,  Big government, Tax and Spend, moderate. He has accomplished next to nothing over the past decade,  except to superintend a presidential campaign that handed the Dems super-majorities in the House and Senate and gave us our first Rogue President.