A person can live without alcohol. Abstaining from it would not put a person's life at risk. Alcohol is ingested orally; it is not intended to be infused intravenously.
A person cannot live without an adequate blood supply. Abstaining from blood needed to maintain bodily function (for example, after a car accident where the individual loses 50% of their blood volume) results in hypovolemic shock and multi-system organ failure and the person dies. Blood can be ingested orally, by which it serves a nutritional value. It does not maintain its capacity to oxygenate the body once in contact with digestive enzymes. When infused intravenously, via blood transfusion, blood has the ability to oxygenate tissues that have been starved of oxygen during the episode of blood loss. It transports glucose and oxygen to the brain to sustain brain function during a critical situation in the person's life.
When faced with the dilemma of whether it is better to die while Keeping Integrity™ to the WTS or accept a blood transfusion and be considered tainted or be Disfellowshipped™ to save your own life, I like to refer to this scripture:
There is hope for whoever is among the living, because a live dog is better off than a dead lion. ~ Ecclesiastes 9:4 (NWT)
Ironically, Ecclesiastes 9:5 is a favorite among JWs and it astonishes me than most of them have never clued in to the context of the previous verse. "For the living know that they will die, but the dead know nothing at all, nor do they have any more reward, because all memory of them is forgotten."