Well, at least he wasn’t Flower.
The Virginia Judge (1935) with Marsha Hunt, who is still alive and kicking at 103.
She made 12 movies before 1939, and is the oldest living member of the Academy of Motion Pictures Arts and Sciences, and the last surviving actress from the ‘golden era’ of films pre-WWII. I think she wins.
Tommy Kirk’s passing earlier this week eliminated or greatly winnowed the surviving casts of many old Disney movies from the 50s and early 60s. Among his many credits, I believe he was the last surviving principle cast member at least of Swiss Family Robinson, The Absent Minded Professor, and Son of Flubber. His death also appears to leave only one surviving principle cast member from Old Yeller, The Shaggy Dog, Babes in Toyland, The Misadventures of Merlin Jones and Bon Voyage!
I’m sure there are many more that could be added to the list, he had a prolific career as a child and teenager. However, his career with Disney came to an abrupt end in the mid-60s when studio executives discovered that he was gay. RIP.
Didn’t those last two feature Nancy Olson?
I decided to check Patton, from 1970. The Wikipedia page lists 21 actors from the film. All have passed on except for Stephen Young (and I don’t even remember his character) and Tim Considine, who played the soldier Patton slapped that got him in so much trouble.
Completely missed that she was still alive. So move those two into the “last surviving cast member” group!
It looks like she’s also the last surviving cast member of Sunset Blvd. It’s crazy to think that there’s still an actress alive today who co-stared with Cecil B. DeMille, who himself was born during James Garfield’s presidency!
Yes, I put up that post on 8 September, right after CHCH in Toronto started showing episodes of The Andy Griffith Show five afternoons a week.
I admit I was kind of uneasy about it when I saw Betty had just celebrated her 95th birthday (you know, synchronicity and all). But this is not as bad as the time my daughter and I were watching a short bio of Leslie Nielsen on AMI’s Famous Canadians series. She asked “Has he died?” (rather than “Is he still alive?” as I erroneously wrote elsewhere), and a quick Internet search showed he was indeed still among the living
The next day, he kicked the proverbial bucket. . 
Murderer!
Didn’t mean to. 
Ages ago I was in San Francisco and picked a tourist pamphlet. On the back was a white space and Compliments of Mayor Moscone’s office. rubber stamped into it. I thought, “Jeez. Can’t they even pop to have it printed instead of stamped? When’d the next election, anyway.”
Two days later Moscone, along with Harvey Milk, were shot dead by Dan White.
Manslaughterer!
With the passing of Eddie Mekka, A.K.A. the Big Ragoo, that leaves Cindy Williams and Michael McKean as the only ones left from the original cast of Laverne & Shirley. As long as we don’t count Leslie Easterbrook who was only on the last two seasons.
And now Mike Nesmith is gone, so the Monkees are down to Mickie Dolenz.
One little Monkee sitting in a tree…
Todd Bridges is not only the last surviving cast member of Diff’rent Strokes, at age 56, he may be the youngest “last remaining (original) cast member” in the thread.
Has a show more recent than Diff’rent Strokes lost all but one cast member? That is awfully quick. Even stranger since it feature young people.
The Golden Girls?
As I mentioned upthread on Different Strokes, it depends how you define "cast member.” Mary Jo Catlett was a series regular over the back half of the show’s run and is still alive (and still working at the age of 83). Shavar Ross (Dudley) and Danny Cooksey (Sam) are still alive. Both were in 40+ episodes.
But to address your question – MacGyver only had two regular cast members in Richard Dean Anderson and Dana Elcar, and only Anderson is still alive. Bruce McGill had a prominent recuring role though and he’s still around.