I've read where Veronica Roth says that by the end of Insurgent, Tris will not be the same girl she was at the end of Divergent. I think this is necessary, and Roth has never shirked from necessary choices. Tris can't be the same. At the end of Divergent, she had discovered her own strength and yet, she had also found her own invincibility. Her choices have been clear. Yes, she killed Will. Yes, she did not forgive Al. Yes, she let her mother die. Why? Because she could see that these choices were necessary, whether or not she could articulate the reasons.
But this is war. In Insurgent, we are promised that faction lines will cease to be the defining factor of good and evil, that those who seem good or evil will turn out to be otherwise, that reality will screw them all over as reality is wont to do, and this is something Roth has never flinched away from. I expect the Tris at the end of Insurgent to be different: she won't be a girl, but a woman. She won't be an optimist, but a realist. She won't be invincible, but she sure as anything won't be vulnerable.
Actually, I'm quite looking forward to it.