My point in all this discussion about timelines is, once again, that it makes no sense for Michael to have waited 5, 6, 7, or more years to avenge whatever it is that he considered he was avenging or to, simply, assume control of the entire NY underworld. Anyone of us can think of any number of variables that could accrue to the passage of that much time including Michael's death or serious illness or injury. Also, consider this. What if Vito had lived to 70, or 80, or 90? Would Michael eventually eschew his quest for revenge or would he just say "to hell with it, I'm going after them anyway?" Of course, during the interim, Barzini, Tattaglia, Cuneo, and Stracchi all could have bitten the dust.