Why Lelouch's life would not have turned out differently if he did not met CC

Lelouch said to CC that he intended to do what he did even without Geass. Ultimately he would have still seek the way towards the power over the world and circumstances.

Ultimately both Kallen and Shirley were as much of his "destiny" as Kaguya was. Out of three Kaguya was the most self-aware. All three of them played their own delusion about being his one and only. They themselves wanted to be with him, but they had nothing of what Lelouch wanted. None of them managed to understand them even in the end.

At the very end, shortly before her death, Shirley did commit to abandon her previous life and enter Lelouch's world of insurrection (rebellion). There was a subtle, but clear change in her way of thinking during her last episode. However, we did not get to see how that could play out: how much Shirley could have become even like one of the girls on Ikaruga.