Well the guy was in his 79 to 80 years, he probably will dead in short order, and his assassination was a symptom, not a cause to the great schism that occur after his dead, so I expect that pretty much nothing change
It would depend on your perspective of the character of Mu'awiyah I and Amr ibn al-A'as. Some say that these two schemed issues without knowledge of each other. Mu'awiyah wished to become caliph and at least maintain the reign of the Umayya of which Uthman was part of. Amr ibn al-A'as wished to monopolize and cnetralzie his power in Egypt at the expense of the Syrian and Iraqi factions that were growing within the Caliphate. If you believe this, then the catalyst for change is not the death of Uthman ibn Affan, though still important, was simply the scheming of either Amr ibn al-A'as or Ali ibn abi Talib against Uthman and the action taken by Mu'awiyah was one centered around his protection of the Umayyad political position. It should be remembered, that the men who killed Uthman, were either men from Amr ibn al-A'as or were from among Ali ibn abi Talib's camp. Mu'awiyah said that the men were from Ali's camp, as they were and these would be the early Shurha or the Khawarij who killed Uthman on account they said, of his unrighteousness and that they accepted only the reign of Umar before him and that rule of Ali ibn abi Talib. They would later reject Ali and would assassinate him; hence their view that the only two caliphs were Muhammad ibn Abdullah, Abu Bakr and Umar ibn al-Khattab.