I don't think the Uchiha were stupid enough to not realize that a civil war would be practically begging their enemies to invade, so they probably never planned to take control through direct military action. They were more likely planning to control people with blackmail and genjutsu, assassinate those who could not be coerced and make it look like the actions of foreign agents or natural causes, and slowly place their own people into positions of power in a plausibly deniable way. If everything had gone according to plan then most of Konoha would never even realize there had been a coup.
Unfortunately Itachi (and Shisui in the anime) betrayed the clan to the Hokage and put them in an untenable position where a direct confrontation was extremely undesirable, but they could not just go back to their old relationship with Konoha once their treason had been revealed. Which is probably why peace talks with the village seem to have lasted for at least a few months, as neither side wanted to start a bloody fight that would endanger Konoha itself but they also could not just forgive and forget such a huge breach of trust.
Anyway if Itachi refused to act against his own clan then peace talks and the cold war between the village and the Uchiha probably would have continued for a good while longer. Perhaps they would have eventually come to a mutual agreement and the Uchiha would reluctantly be given more influence over the village government, but also required to put up with more oversight from the village. Perhaps Hiruzen would defuse the entire coup by making Itachi the next Hokage, which would satisfy all the Uchiha's demands while also knowing that Itachi would not abuse his power and would rule the village fairly. Perhaps talks would have broken down and a battle would have broken out between the ANBU and the Uchiha that would cripple the village and put them at a disadvantage to the other major villages. Perhaps Danzou would have gone behind the Hokage's back and attacked the Uchiha, provoking them into battle in he hopes that he could take over the wreckage, much like he intended to do when Pain invaded. Perhaps Danzou would use Shisui's eye to make the Uchiha submit to the village and accept second-class citizenship. Perhaps Obito would have acted on his own and the Uchiha clan would have been wiped out anyway but without Itachi's help. There's really so many different ways this divergence could go.
Unfortunately Itachi (and Shisui in the anime) betrayed the clan to the Hokage and put them in an untenable position where a direct confrontation was extremely undesirable, but they could not just go back to their old relationship with Konoha once their treason had been revealed. Which is probably why peace talks with the village seem to have lasted for at least a few months, as neither side wanted to start a bloody fight that would endanger Konoha itself but they also could not just forgive and forget such a huge breach of trust.
Anyway if Itachi refused to act against his own clan then peace talks and the cold war between the village and the Uchiha probably would have continued for a good while longer. Perhaps they would have eventually come to a mutual agreement and the Uchiha would reluctantly be given more influence over the village government, but also required to put up with more oversight from the village. Perhaps Hiruzen would defuse the entire coup by making Itachi the next Hokage, which would satisfy all the Uchiha's demands while also knowing that Itachi would not abuse his power and would rule the village fairly. Perhaps talks would have broken down and a battle would have broken out between the ANBU and the Uchiha that would cripple the village and put them at a disadvantage to the other major villages. Perhaps Danzou would have gone behind the Hokage's back and attacked the Uchiha, provoking them into battle in he hopes that he could take over the wreckage, much like he intended to do when Pain invaded. Perhaps Danzou would use Shisui's eye to make the Uchiha submit to the village and accept second-class citizenship. Perhaps Obito would have acted on his own and the Uchiha clan would have been wiped out anyway but without Itachi's help. There's really so many different ways this divergence could go.
