To my dearest compatriots, who have recently honored me so much by electing me a member of the Parliament where so many agreements should be adopted of utmost importance to the destiny of our Revolution, I am saying that I will neither aspire to nor accept — I repeat, I will neither aspire to nor accept — the positions of President of the State Council and Commander in Chief.You can read the whole thing here.
He'll still be a looming presence over the Cuban body politic, and it's almost certain that his younger brother Raul will be selected to replace him. I'm not expecting any dramatic changes, unless somehow Castro's resignation motivates the Cuban people to revolt. At this point, after over fifty years of heavy-handed Communist rule, the state's instruments of power are stable institutions – and therefore very difficult to remove. Without external help, it would take something of a miracle for a democratic state to emerge...