It was sad to hear about all those three. But shucks, they all had good careers and, I hope, good lives.
I remember Don Knotts as far back as the old Tonight Show with Steve Allen in the 50's. His 'nervous man' act was well polished even then and was hilarious.
Dennis Weaver was great as Chester Goode on Gunsmoke. But he was cursed with a character who couldn't bend one leg and almost got really crippled a couple times doing some difficult scenes. (He must have been glad they changed the last name of Chester for the tv series. On radio, it was Chester Proudfoote.  )
Darren McGavin is the one I will miss the most. He had an awesome screen presence. He nailed the satiric role of American Dad so well in 'A Christmas Story' I think it will live forever.