Well TB, there have been any number of Dons murdered and their former criminal enterprise continued. Given that II never identifies any other families at least around New York, I don't know if any other family would have moved in. I doubt that the Rosatos would have had what it takes to do so. Could Neri and Rocco have taken the reins of the family. Of course, Frankie was in command of the New York troops at the time. Was he formidable enough to fend off the Rosatos or anyone else? Would he have cooperated with Neri?

For storyline purposes it would have worked out, but having an outsider like Roth murder a Don (or even try to with impunity) is rather suspect.