And what if you might be able to make decisions again tomorrow. Or the day after? Or in two weeks time.. ? These things are never all that 'clear'.
Is it better for 100 families to live for years with a vegetative loved one with the most realistic hope being that a few to emerge profoundly affected and never their full selves again, or is it better for those hundred families to get to grieve?
The pain of a loved one's continued quasi-existence, plus the difficulty of their life if they ever are to recover, make it so that the compassionate personal choice is to say "once the best estimated probability of my recovering robustly is clearly below P%, let me go". The value of P is a decision to be made carefully, and with deep consideration for ourselves, our loved ones, and for all of humanity.
Edit: note this might be different for you. You are the only one who can make that call. You can also decide that you want to be kept alive as long as possible. But then at least your loved ones know that that's what you wanted.