Then no Social war. Marius would still try to gain command for the war against Mithridates, and having no army at his immediate disposal, Sulla could do little to oppose him. If Marius succeeds in being sent in the East, and OTL showed it was entirely possible, then he could die in the middle of the campaign of old age. Another commander, maybe Sulla, would be sent by the Senate, however it’s also possible, and perhaps rather probable, that Marius’ army could pick its own commander, like the Fimbrians did, opposing the central government’s decision. At Rome, Cinna could very well still be elected consul, thus repeating OTL’s events with the siege of Rome and its capture by the Cinnans, only this time Marius doesn’t lend his name and person to his cause. Cinna would then try to send a commander loyal to him, Lucius Valerius Flaccus in all probability, to gain command of the army East, or he could try to deal with that army’s new commander, who would probably be a man hostile to the optimates, or maybe, if Marius is still alive and in command, Cinna would simply swear allegiance to him and elect him consul in absentia as the Senate did at the time of the war against the Cimbri and Teutoni. All in all, Sulla’s dictatorship would be butterflied away. What Cinna’s plans with his government were exactly is difficult to assess, but probably we’d see an early rise of the people outside the noble and most prominent families. Men like Sertorius could hope to become consul. Pompey would stay friends with Carbo and, in due course, also become consul. Caesar, being the son in law of Cinna, would be particularly favored for a successful career. Crassus, however, would have no such luck, and I doubt that under Cinna he’d become as powerful as he was IOTL. Whether Cinna’s government would have collapsed beneath his feet, or endured and survived at least until his death, it’s impossible to tell.