Loving the inpute on this. Keep it coming. Personally I believe he becomes the "Don" after Ciccio for a three reasons. He has already helped the widow(like a senator or president watching out for other people), earning respect from his peers killing Fannucci), and avenging, not 1, not 2, but 3 personal insults to him(the killing of his family and then killing Ciccio).

mafioso: to make oneself respected; to be strong enough to avenge yourself for any insult to your person, or any extension of it, and to offer any such insult to your enemies
--Pino Arlacchi