I would suggest looking at what happens when the body, or more specifically the information stored in the brain is damaged... If the person is more than just the information stored in the brain, the I would suggest that the damage or loss of information would have no effect upon the person.
I know from experience that if there is degradation in the information stored in the brain, then we have a stark and often upsetting change in the "person" I once knew. This has a profound effect upon how I view what makes a person, a person! 
To those around them yes, upsettingly so, but It's a bit of a catch 22 or vicious circle. A brain injured or degrading individual may have perfect reason, consciously to themselves, but the outward manifestations of their disease may result in gobbledegook speech or noises that result in feedback frustration to the individual. Wouldn't that cause you to shutdown, go crazy or hit out!
We guess or hope that people in those situations are vegetables. Unfeeling incognisant. The alternate is unthinkable but unfortunately probably closer to the truth, when you examine the enlightenment of discoveries of bad CP sufferers or stroke victims. Everything is okay intellectually on the inside but the interfaces are scrambled. Input and output. Determining intelligence and sentience is impossible as our measures are based on inputs and outputs.
As long as we think, we are. We are not just the inputs and outputs of a moment in time. We are what we are on the inside and what we have done, achieved, become. We need to be mindful of what those individuals are to themselves and not just to those around them in the current state.
This thread has become very depressing now. Mia culpa!
Amigas don't think. They are what the