It wouldn't have stopped the Uchiha coup. Regardless of Danzo's schemes, the Uchiha were planning a coup. Itachi waited as long as he possibly could, same thing with shisui. Shisui at the end of his life agreed that their was no other way to stop the coup. Danzo definitely stopped Shisui from stopping it by stealing his eye, but after that there was no stopping it in a way where people weren't going to die.
But how do I think the fight would end? That is a different situation. It depends on whether Danzo has KA or izanagi at this point. If he has both I think he would probably beat hiruzen. Danzo is definitely powerful, and was going to be made the 6 hokage, don't forget that. Being able to die 10 times and cast a genjutsu on Hiruzen that is supposed to belong only to shisui would likely surprise Hiruzen and give Danzo the edge. Without KA or izanagi, I would say that Danzo loses to Hiruzen, but its a good fight. I don't think Hiruzen would lose any limbs, but would be wounded and likely have to be put in bed for awhile. Which would be a perfect time for the Uchiha to exact their coup.