You would have seen an earlier civil war as by 65 Nero was one of the few remaining men of the Julio Claudian dynasty and extended family.
Most likely even if piso tried to become Emperor you probably would have seen a huge vieing for power that could have broken the Empire, most likely Corbulo would try for the throne as would one of the danubian governors and one of the rhine commanders. Vespasian unless he gained a post somewhere with an army most likely would not come out as Emperor unless the civil war became an interregnum for many years with a state like the crisis of the third century