“The cemeteries/graveyards are full of indispensable men/people” means that no one is indispensable. The saying has been credited to Georges Clemenceau (1841-1929) and Charles de Gaulle (1890-1970).
   
“The cemeteries are full of indispensable people” has been cited in English since at least 1948.
 
     
Wikiquote: Charles de Gaulle
Charles-André-Joseph-Marie de Gaulle (22 November 1890 – 9 November 1970) was a French military leader and statesman. During World War II, he reached the rank of Brigade General and then became the leader of the Forces Françaises Libres (“FFL” — the “Free French Forces”). Between 1944 and 1946, following the liberation of France from German occupation, he was head of the French provisional government. Called to form a government in 1958, he inspired a new constitution and was the Fifth Republic’s first president, serving from 1958 to 1969.
 
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The graveyards are full of indispensable men.
. Les cimetières sont pleins d’hommes indispensables.
. Sometimes attributed to Georges Clemenceau. In fact, Clemenceau seems to have said Les cimetières sont pleins de gens irremplaçables, qui ont tous été remplacés.
 
Wikiquote: Georges Clemenceau
Georges Clemenceau (28 September 1841 – 24 November 1929) was a French journalist, physician and statesman. He served as Prime Minister of France from 1906 to 1909 and from 1917 to 1920. He is remembered for his wit and his wartime leadership of France during World War I.
 
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The graveyards are full of indispensable men.
. Sometimes attributed to Charles de Gaulle.
 
Google Books
A Man of Means
By Jacques Nels
Chicago, IL: Ziff-Davis Pub. Co.
1948
Pg. 111:
The cemeteries are full of indispensable people.
 
Google News Archive
13 August 1957, Toledo (OH) Blade, “‘Indispensable’ Parker Quits; Wilson Takes Over” by Dave Diles, pg. 23, cols. 1-2:
DETROIT, Aug. 13 (AP)—George Wilson, an assistant coach for eight seasons, today was named head coach of the Detroit Lions, succeeding Raymond J. (Buddy) Parker who resigned in a surprise move last night.
(...)
Early today Parker reaffirmed his stand, saying “the cemetery is full of indispensable men.”
   
Google Books
The Welfare Staters
By Victor J. Fox, pseud.
New York, NY: Freedom Press
1962  
Pg. 380:
No public official is indispensable; Arlington National Cemetery is full of ‘indispensable’ men.
 
Google Books
Reporting India
By Taya Zinkin
London: Chatto & Windus
1962
Pg. 127:
... told me when I asked him the usual haunting question about India’s future leadership, and he added with a shrewd grin on that wrinkled tortoise face of his: ‘Cemeteries of the world are filled with the bones of indispensable men.’
       
Time magazine
France: Close Victory
Friday, Nov. 02, 1962
(...)
Opposition posters quoted the words of the late Premier Georges Clemenceau: “The cemeteries are full of indispensable men.”
   
Google Books
Challenges in India
By Taya Zinkin
London: Chatto & Windus
1966
Pg. 11:
“The cemeteries of the world are filled with the bones of indispensable men,” Sardar Patel told me shortly before he died.
 
Google Books
General Marshall Remembered
By Rose Page Wilson
Englewood Cliffs, NJ: Prentice-Hall
1968
Pg. 272:
In the Army we often scoff at the myth of the indispensable man, for we have always maintained that Arlington Cemetery is filled with indispensable men.
   
Google Books
The French:
Portrait of a people
By Ted Morgan
New York, NY: Putnam
1969
Pg. 140:
“The cemeteries are full of indispensable men,” was a typical Parisian reaction.
 
Google Books
Castello Branco:
The making of a Brazilian president
By John W. F. Dulles
College Station, TX: Texas A & M University Press
1978
Pg. XVII:
And he repeated with wry wit the famous words of Rivarol: “The cemeteries are full of the bones of irreplaceable persons.”
 
Project Syndicate
And Free Flows the Nile
Jaswant Singh
2011-02-17
NEW DELHI – For 18 days, during the ebb and flow of protest, it did not seem possible that the end of the Egyptian Revolution would come so suddenly, in a terse announcement that lasted no more than a half-minute: “President Hosni Mubarak has relinquished office….” With that, amidst roars of victory, an era was ended, reaffirming the old saying that “the graveyards of the world are full of those who considered themselves indispensable to their nations.”