As interesting as I found this scenario, I also felt very confused. I was very happy to see a healthy, well-fed Mama snake in our yard. At the same time, salamanders are adorable little critters, and I've come to love interacting with them so I felt very sad for this poor, dying one.
It definitely is not a fair fight here. Salamanders are a whole bunch slower than a snake and definitely weaker. The only thing this amphibian has going for him is the fact that he rarely comes out during the day and prefers to stay hidden under a rock until nightfall when the dew starts to settle.
It was my daughter and I who got an unexpected lesson in ambivalence that day. The fact that it was too late too make a decision about whether or not to save the salamander was a good thing. We walked away saying, "That mama needs all the energy she can get. We will save all the salamanders we can from the shop, the garage and even the road.". And so, we were good. We placed Mama snake where she was better hidden from our local hawks, because she could barely move herself and would make easy prey. I guess you could argue that we shouldn't have done that, and that now some poor hawk would be deprived of his lunch because we had stepped in.
It's moments like this I love to remind myself that I am also a part of nature, and if I wasn't supposed to be there to make a decision, I wouldn't have been. Humans are way too hard on themselves for their role in nature and the world. Be peaceful, kind and do your best to use only what you need. You can't go wrong.