Unfortunately I know what I'd do, and I wouldn't be too proud of it; I'd be emotionless. A few times, the "family dog" (the dog my father bought for my sisters and expected me to care for) got into trouble and I just thought "Well, shit."
I love her, I really do, I had her for six years. I know if she actually died or was hurt in front of me I would be alarmed, later grieve, but I wouldn't be crippled with fear or heartache. At one point she got into a fight with a Dogo Argentino that had wandered onto the farm. I did pick her up and tried shielding her with my body, my sister opened a door behind me to let me get away with her. The Dogo wasn't a killer, though; she was trying to grab my dog by the scruff and pin her down because my dog was being territorial. My dog threw a fit and tried attacking the Dogo. I had my hands in the Dogo's mouth pulling my dog away. I remember being pretty clear-headed while pissed at my own dog, fully aware the other dog wasn't being aggressive. The Dogo stood up to grab her from my hands, but there was no snarling or fast movement from her, no hard biting; my dog was the one snarling and barking like a rabid animal. The Dogo had a tiny jack russel with her, she didn't think a smaller dog was prey or a toy. Just responded to my dog's asshole behavior. After I put my dog indoors, I led the Dogo up to the road with a hand on her collar and waited for her owners to drive by and take her. She was totally chill, all tongue-out, derp faced. Cool dog.
Since then I've gotten the dog better trained... She still has a strangely high territorial drive and acts like a Rottie when "intruders" are around. It sucks because what training I do with her easily gets screwed over due to her living with my psycho family, she either gets beaten by my father or neglected and teased by my mother/sisters. Best thing I can do is keep her with me outside or have her in a kennel.