Or should 69-year-old Fidel decide that four decades is a long time in politics and opt for retirement, Raul, 64, will be the front-runner among potential successors.
During his visit to the U.N.'s 50th anniversary in New York last month, Castro told interviewers "dying doesn't figure in my immediate plans". The talk on the Havana diplomatic cocktail circuit, however, is that he may be prepared to stand aside when his latest term as president expires in March 1998.
The Spanish government, led by Felipe Gonzalez, has been quietly working to push a transition to democracy modelled on the one that avoided potential civil conflict in Spain after the death of the dictator Franco in 1975. Spain even offered to host President Castro in exile in the north-western region of Galicia, where his father was born. Diplomats involved say he did not reject the offer out of hand.
Cuba-watchers, however, are split over who would replace the man who has ruled since overthrowing Batista in 1959.
In his one specific reference to succession, admittedly 10 years ago and in an interview in Playboy, Castro talked in terms of dynasty. "Since the beginning of the revolution, and particularly when we started realising that the CIA had plans to shorten my life, we suggested the prior nomination of another comrade, Raul Castro, who would immediately assume leadership," he said. "In my opinion, the comrade chosen is the most capable, not exactly because he's my brother, but due to his experience and revolutionary merits."
Cuba has changed since then, though, with openings towards capitalism and the emergence of younger faces within the Communist leadership. Some analysts say a collegiate form of government is a transition option. Others are betting on individuals other than Raul, who is head of the armed forces and No 2 to Fidel in party and government.
Most heavily backed are Carlos Aldana, the party's chief ideologue; Carlos Lage, economics tsar and now effectively prime minister; and the foreign minister, Roberto Robaina,whose expensive silk suits worn over black T-shirts make him look like a Miami drug dealer.
Asked last year whether he might one day succeed Castro, Robaina wisely echoed the stated views of the jefe maximo, but added an intriguing twist. "The Cubans have known it for a long time, based on reasons of history, results and authority. It's Raul. And Raul is not Fidel. He's Raul," Robaina said.
If Raul does take over from Fidel, many believe a more repressive atmosphere will settle over Cuba. Raul is considered a more doctrinaire communist than his brother. He was a stated Marxist-Leninist before the 1959 revolution, whereas Fidel, who had fought on a nationalistic platform, hoisted the red flag later as he consummated his affair with the Soviet Union.
Just after the revolution, Life magazine described Raul as "ruthless" and said his "riflemen, firing at six paces, blasted 71 into a mass grave at Santiago (in eastern Cuba)". Even Fidel was "taken aback by Raul's savagery," the magazine said.
In 1989, apparently fearing that Cuba's most popular and reform-oriented general, Arnaldo Ochoa, could pose a threat to him and Fidel, Raul played a key role in an investigation which led to the general's execution on drug-running charges.
As the Soviet Union collapsed and the end of the Cold War reduced the perceived threat of a US invasion, Raul had already begun using his 300,000- strong armed forces, exempt from revoluionary laws prohibiting sackings, for economic ventures. He concentrated his men on agricultural production, first making themselves self-sufficient, then opening up retail food markets.
He set up lucrative hard currency stores and a tourist venture called Gaviota (Seagull) with its own airline, using redundant MiG fighter pilots.
Raul also has a Yeltsinesque tendency to disappear for long periods, giving rise to rumours that he has a drink problem and is drying out.
"Raul taking over? How ludicrous," said Ninoska Perez, spokeswoman for the Miami-based Cuban-American National Foundation, the biggest anti-Castro exile group. "This is like telling the German people in 1945 that Hitler's brother would be taking over."