She'd have returned to the States, had six kids, none of whom became brats like Mary or effeminate opera singers like Tony, and she would never have bugged Michael to death about his business. Because of that Michael's health would have been better, she would have handled Fredo and/or seen through him for Michael, and at the end she would bask in Michael's triumph when he took over Immobiliare. Did I mention that means he would not have been on the steps of the Palermo Opera House that fateful night?