Your dog will probably have a fear of larger dogs for quite some time, in fear that this could happen again, but it sounds like they were relatively unscathed.
I've played out this scenario before in my head, and I know I would throw myself in front of my dog when danger approaches, even if it were a moving vehicle. It may sound extreme, but I'm not sure I could live with myself knowing that I could have saved an innocent life.
I've actually come close to having to protect my dog. My dog was by my side in our neighbors yard and un-leashed. We were talking with them, their dogs were leashed. All of a sudden the neighbor across the street's 80lb rottweiler got out, and was b-lining for our pack of dogs. This is when something extraordinary happened. As soon as that dog reached our parcel of lawn, my 35lb Sheltie puffed himself up and sort of jumped up and pounced in the path of the rottweiler. That rottweiler put the brakes on so fast and hightailed it back to his yard, I was kind of amazed that my smaller dog had the instinct to make himself look bigger and formidable to a larger dog to send them packing, in hindsight we were extremely lucky.