1. What could have happened
No, Tris did not want to die. But her true abnegation identity made her selfless, so selfless that she sacrificed her life.
What could have been different?
In her final moments as she died she hoped that Four would be comforted by the idea that she still dreamed, she hoped, she wondered. Wondered about the endless possibilities- her starting a life with Tobias,having a child. She thought of how the child would watch her train new initiates and how the eurdite part of his identity would make him curious.
"Mother why do you never hold a gun" he would ponder
Yes Tris was still weakened by the thought of these weapons, but she did not mind...
“Becoming fearless isn't the point. That's impossible. It's learning how to control your fear, and how to be free from it.” she remembered
and as her time drew to a close she pictured Will his untroubled restful face- and she closed her eyes.