I'm truly sorry for this event, OP. As a father, I cannot fathom how this feels, but I have had a taste of it when my young brother-in-law was in a catastrophic car accident. I hesitate to share this story, because it may again bring hope, and I agree that hope is pain in these situations. I do not know the details of your situation and how confident the medical team is in their prognosis. If you are certain in their judgment, then please do not read the rest, because it is hopeful. I share it here, if not for you, then for others. Apologies again if this is overstepping. I will delete it if this is out of bounds.
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My BIL was in a head-on collision with a semi (he was in a Honda Civic) on a snowy day when he was in his early 20s. He was on his way to go snowboarding.
My wife, his only sibling, got the news immediately and we both got on a 5 hr flight to the hospital where he was. My wife was heavily pregnant.
While he was initially conscious after the accident, soon an embolism formed and resulted in a blockage in his brain. As I understand it, the embolism actually should have ended up in his lungs and killed him, but due to an unknown hole in his heart, it ended up in his brain and instead caused a severe brain injury. He lost consciousness and slipped into a coma. His physical body was battered (many broken bones) and now he also had no brain function. Non-responsive.
While grieving the accident, and his loss, we met with several Drs. at the hospital and their prognosis was bleak. Even on the slim chance that he would survive, he would not ever walk, or talk, or do much of anything ever again. I also remember the dire moment when the brain MRI came back and it looked like one big cloud of fog. I had spent a career at that time in medical imaging and while I was on the engineering side, I knew this was a horrible sign and the doctors confirmed that. One doctor matter of factly and without mincing words told us we'd be best off pulling the plug soon, so that his organs could be used. We could not bring ourselves to make that decision at the time (I often wish I could remember that Doctor's name to update him on what has transpired since, but alas that whole period of time was a grief-filled haze).
He stayed in that coma for 5 months, slowly showing signs of responsiveness. Eye movement, for example. Eventually, he "woke" up, but could not speak, still not walking or even able to sit up. Over years of intense therapy and effort by him and his team (and my wife supporting all of the above), he slowly improved. All of us spent so much time talking to him, while getting little to no response back. Eventually, you could get to the point where you told a joke and he would muster a smile, maybe with his eyes at first, and then with his mouth. I still remember the day the hospital called and the nurse put him on the phone to my wife with shock to say that he had said a word and he said "I love you" to his sister. Mind you, it was very hard to understand him (and he still is a bit difficult to understand, to this day).
I don't want to write a novel about this (I could easily), but his progression continued, over years and years. Physical therapy, speech therapy, occupational therapy and more. Today, a decade later, he can walk, talk, play video games, go to the movies, he does activities like swimming and skiing with assistance from equipment and aides. He lives in an apartment that has care aides around when he needs them, but can do many things for himself. He has the mentality of roughly a 10 year old, in some ways, but he has memories of his life before the accident and maintains his old sense of humour and love for his family. He is still with us and big pieces of the "old" him are there. He is a wonderful uncle to our children, the oldest of which was weeks away from being born when his Uncle's life changed forever.