"'E's kicked the bucket, 'e's shuffled off 'is mortal coil, run down the curtain and joined the bleedin' choir invisible!! This is an ex-tyrant!!"
Here is my first-blush opinion. First, the original announcements from Havana said that Fidel's surgery was so serious (he's 80) that he had formally turned executive authority over to his lsightly-younger brother, Raul. Raul was already "the second-ranking member of the Cuban Council of State." That means he was Cuba's numero dos to begin with. As has been reptitively noted by others, there is no prior record of any such transfer of power from Fidel to Raul or anyone else.
Since the Cuban health minister has said that Fidel's recuperation is expected to take 4-6 weeks, one wonders why a formal transfer of power was needed at all, when the transfer recipient was (a) already second in command of a dictatorship and (b) the brother of the number one. Raul has long wielded considerable executive authority already. For such a short time Raul would already be the go-to man for the government.
Dictators are usually loathe to designate a successor for fear that once they surrender power, even temporarily, they won't get it back. Maybe Fidel had no such fears about his brother, but that leads to the second curious thing about this matter: Raul has not been seen nor heard from since he supposedly took the executive chair.
Fidel stopped doing day-to-day administration of the government decades ago. With the structure of the revolutionary government long established, it's doubtful, IMO, that Fidel has exercised executive authority except for crises, state security matters or long-range planning guidance in many years. The management of the bureaucracy is done by others. Besides, Raul has been "Minister and Maximum General of the Revolutionary Armed Forces" since 1959, which means he already had control of state security.
That being so (if it is so) then it buttresses my thought that there was no especially compelling reason to make a formal transfer of power. Raul would have continued to do what he has been doing for decades with little effect over just a few weeks.
But neither Fidel nor Raul have been heard from since July 31's transfer-of-power announcement. Surely just an appearance on Cuban television by Raul would have been advisable, if only to remind the people that they shouldn't get wrong ideas about what Fidel's absence meant.
My guess: Fidel is in cold storage, having died suddenly of natural causes. Alternatively, the announcement of his surgery may be true, just late, with his death occurring during or shortly afterward.
As for Raul, I dunno, but I'd not be surprised if he also died suddenly - of lead poisoning.
So who might really be running the government? I have no idea. That's the weak link in such speculation. If Fidel is really dead - and Raul either also dead or under house arrest - then we'd expect to see a real struggle going on for power among the rest of the Cuban dictatoria. It wouldn't be possible to conceal it because it would inevitably involve maneuvering for control over the armed forces, who historically have settled the outcome in such situations.
To borrow Winston Churchill's observation about the Soviet Union, Cuba is "is a riddle wrapped in a mystery inside an enigma." And there things rest for now.