So tough. I know I would want to keep her alive if it was so easily done with a blood transfusion, and I know how important it would be for her to observe the Watchtower Bible and Tract Society's commands on this issue.
Ultimately though, I advocate for the right of people's freedom to life. That includes the right to end their life if they so choose. I know that I wish there were government-sanctioned assisted-suicide clinics such as are in Switzerland. So I would.
This question doesn't apply to me though. My mother's medical decisions will be made by her husband. If they both are incapable of making a call, they have witness friends set-up as powers of attorney. It also doesn't help that I live 3000+ kilometres away.