The issue is not easily resolved. Nero had become deeply unpopular with the upper classes for his blatant un-roman behiour, outrageous money making schemes, and grandiose self absorption. As at any time in the latter half of Roman history, any perceived weakness or lack of opularity invites ambitious men to conspire or mount coups, especially since the communication disctances to provincial areas and the availability of standing armies loyal to personality and paypacket rather than patriotism, was all the more dangerous.
Nero had been for a long time trying to push the Senate down. It's believed by some that whilst the Great Fire of Rome in 64 was an accident, it was further enflamed by conspiracy in order to destroy the homes of the landed wealthy in Rome, where all the political dealing was done behind closed doors. Very much "An act of God" then .
For these reasons it's not beyond speculation that a great many senators were already conspiring to get rid of the Caesars and restore full republican rule - they had almost done so earler after the death of Caligula, but the Praetorians intervened and installed Claudius to safeguard their jobs. People routinely assume that the Republic had finished and Empire begun with Augustus - that's merely a historical convenience and not a condition of political reality. There was a Roman empire during the late Republic, and the Empire still called itself a Republic with most of the institutions still intact to some degree. Caesars were not absolute rulers either - their powers were granted by the Senate, though obviously in some cases the reasons a particular man came to power meant that giving them the power they wanted was a better bet, and then again, in the case of rulers like Nero, some simply ruled as if they were absolutely in charge regardless of the actual situation.
So could the Empiure have split in 69? yes, it could have, but note that none of the usurpers stayed in the provinces and set up a breakaway state. They all headed for Rome and fought it out, or perhaps took advantage of a situation. So in reality, sooner or later, someone was going to take control of Rome and its provinces. It really was a case of winner takes all.