Why won't Jehovah's Witnesses accept blood transfusions, even when their lives are in jeopardy?

Who can guarantee that a blood transfusion WOULD save a persons life? I have heard of many that have died despite having a tranfusion! There are NO guarantees. Besides, if our life WAS saved, because we disobeyed God's command, of what point would it be to continue "living"? We DO accept transfusions, just NOT tranfusions of BLOOD. We accept substitutes, because basically it is the fluid volume that needs to be replaced. We take the best care of ourselves, and we value the hard work of doctors, etc. We just refuse to break one of GOD'S laws. Who are WE to question HIM? My brothers and sisters have given you enough scriptural proof as to what those commands are. Some people just love to try to find fault with those that are only trying to live up to Jehovah's high moral standards.