Slicing the lungs alone will take some time to cause the deer to die from lack of oxygen. Even with damage to the lungs they are still able to process some oxygen to the blood. It is blood loss that is the main kill mechanism and there is some change that a broadhead will miss all major arteries and veins. My father double lunged one in the early 90’s that went 1.5 miles. I shot one in 2002 that sliced that back end of both lungs and he lived almost 6 hours. When we opened him up to gut him both lungs were completely full of blood, it just took a long time for him to bleed enough. Is it extremely rare? Yes. Is it impossible? No.