Allegiant: What should have been the ending

I see Cara, standing to the side, her face has a bandage on it and I flinch. But that is not the only reason why, Cara has a troubled look on her face and her eyebrows are knitted together, as if wondering how to say something. "Cara" I ask cautiously, "What's wrong?" She turns and her eyes are wet. Something bad has happened, I know it. "Tris.." she gasps, "She went into the weapons lab instead of Caleb, she was shot and she didn't survive. I am so sorry Tobias." Most of the time I can tell when people are lying and I think this is a lie, Tris wouldn't leave me in this world alone...this is all just a prank, right? Then it hits me, of course Tris would go into the weapons lab instead of Caleb, of course she would... A tear rolls down my cheek and I can't support my grief yet I keep standing. Christina however, hunches over..crying. I stumble through the doors and make my way to the weapons lab, unable to cry. I don't know why I am going there, I can't save her now, she is dead. I can't bear to see her body but I need to know who killed her. My feet stop and shuffle at the direction my brain wants to take. To be honest, I don't know where to go, what to do, if I should live. I find myself in the control room, I sit in an empty seat and stare at the screens. Eventually, my eyes find the Weapons Lab security screen and I see Tris, dead and lying on the floor. I let out a strangled cry and bury my face in my hands, weeping. I cry for her, like she would cry for me. I gasp and fall to my knees, sliding off the chair. But I need to see what happens, who I will kill for killing her. Tears are still falling down my cheeks but I sit up. I rewind the tape and see everything. My Tris, she blows down the door and is engulfed by the death serum. She falls and I realise why, she is not wearing a suit, she can't survive the serum, she will die. My eyes widen and my mouth shouts to her, telling her to stop that nonsense but no words come out. I watch in horror as the death serum kills her slowly, watching her squirm in pain. I turn the chair and croak out her name when all of a sudden I hear my name. I whirl around to the screens and see Tris mutter my name. My heart breaks, she was calling me moments before her death. I see her breaths falter and I lose faith, then I hear my name again, "Tobias, I love you." My heart rips again as I watch her fight the serum, struggling to survive. But I know she can't nobody can resist the serum, GP or not. And even with a suit you only get a few minutes of life. I look closer and gasp. Tris is getting up, alive. She fought the death serum....it  didn't kill her...but how on earth?! There is no explanation for this and there never will be for she is.....dead. It is as real even when I say it in my head. My Tris is dead. She is gone for eternity. I will never look into her eyes again or see her smile. I won't ever see her move in reality. Tris stands tall and strong despite the death serum and she smiles. She walks over to the button when I see a figure...a figure with a gun. My heart starts to beat and I panic. I grab my hair to keep my mind from whirling. I can only watch, terrified as the figure aims at Tris. She hears the click of the trigger and her eyes widen. She turns her head slowly, and yelps. "David?" I hear her croak, her voice is a rough whisper. Slowly, the serum starts to fade and I can make out  David, Tris' mother's friend killed her daughter. He killed Tris. They talk for a while and the gun never leaves Tris. Her eyes start to fade and I cry as I see her hope shatter. I try to manipulate 'screen Tris' to tell her to run away, further away from David. Further away from death. But this is Tris I am talking about, the girl who whipped my dad to protect me, who let me throw knives at her, who saved me and who saved Caleb. I know in that instant she will not leave. I hear a gunshot and scream. Tris is in pain, a bullet lodged in her arm. She screams but even that can't prepare me for what I see next. She reaches out to either balance herself or continue to do the mission. David shoots again and I hear a blood curling scream , Tris is on the floor, curled up, shaking and I realise he shot her in the ribs. I zoom in despite the circumsatnces and scream. It hit her heart I am sure of it, or if not, it narrowly missed. I zoom out again afraid and then my eyes widen. She continues to proceed. David fires again and shatters her shoulder. Tris' eyes are pained and full of remorse and regret but she knows it is too late for her. She releases the serum and collapses to the ground in a heap, dead at last. 

David slumps in his chair but I can not take my eyes of Tris, limp and broken. I need to carry her dead body, not some stranger..I loved her, I will get her, dead or alive. I leave the control room when my steps falter, do I really want to see her body, I am furious at myself. After all we did together, I am hesitating to go see her? I am a coward, she deserved better... I am scared for her. she is all alone in a dead world but she will be with her parents and will and Lynn and..I shake, Uriah.The lab is in sight, I near the last place tris was. I cry out in horror as I see David in the chair. I need to kill him. he will not live. he must die. but the thought of Tris keeps me going. She lies on the floor, her hands and knees brought up against her chest. as if to keep the pain away. Her eyes are closed and blood is still seeping from her wounds. my eyes dampen and I can't breathe. why didn't I die, why tris. why her? she deserved better...I need to touch her, to hold her I'm my arms. I bend and slide my arm under her cold, still legs. I slowly and gently carry her, even though I know she can't feel a thing. my tears falls down and splash her face. I am crying. I never cry bit I am crying, for her...for my tris. my fingers skim her bullet wound and I flinch. the pain she must have felt... I shake and hug her to my chest. "Tris, I love you!" I cry. then, I hear a moan. I jolt and gasp. I look down at my tris and see her eyebrows move, but only ever so slightly. "She's alive!' I scream. I run now, ignoring her gasps and groans of pain. I near the hospital and burst through the doors. almost immediately a flock of doctors pry tris away from.me and furiously work on her. my mind is swirling...she survived, she cheated death. I can't imagine the pain she must be in, her whole body paralysed with pain. I sit outside the room, my breaths fast, what if they can't save her..what if she is still gone?

It has been a month since Tris was found alive and put in the hospital but still I am not allowed in. The doctors come out sometimes and when they do, it is never good news. Realisation kicks in, Tris is still as good as dead. They say she is unconsious and has been all month. They say she hasn't even moved once. She is in a coma, she doesn't have any percent chance of waking up. They have worked on her for the past month and have made basically no prgress in getting Tris back to normal. I sit in the chair outside her room, my eyes wet. A doctor comes out and addresses me. I walk towards her as she starts rambling on in a foreign language. "English" I say weakly. She stops and smiles at me. But then her smile drops and her face takes on a more sad, troubled look. She whispers, "We can not save her, we are taking off her life supply today." I let out a cry but choke it down. The woman eyes me with sadness but then clears she clears her throat, "