Normally, I don't give these kinds of rumors any credence, but something in the Washington Post lends me to believe something might be up. From the Washington Post:
He has asked that planned celebrations of his birthday be postponed until Dec. 2, the 50th anniversary of Cuba's Revolutionary Armed Forces. Castro and the rebels he led landed on the southern coast on that date in 1956, eventually taking power in 1959 after dictator Fulgencio Batista fled into exile.
That would definitely be a opportune time to consolidate power should Fidel prove to be dead. Guess we'll have to wait and see.