Daniel, interesting thread. I just had this conversation with my 18 year old. We have both decided to take blood if absolutely necessary. We have not informed the ardent JW in the house about this, as would cause him anguish. My 18 yo and I have decided to back each other up if this horrible event occurs.
One thing to remember is: all the animals sacrificed were killed, their blood was drained out, so yes, their life was in the blood. When humans donate blood, they don't sacrifice their lives to do it. To me, that is the biggest difference there is. Jesus died, so his life was a sacrifice, donors don't die because they gave blood.