Hi Kathy,
This is a subject that I have involvement in, and we are talking about this one case. In THIS case, the one that we are discussing here, in this thread, the snake had lost its lower body. ANY gut wound where the entrails are ruptured or the snake has had it's lower body 'amputated' north of the sexual organs and cloaca, is a dead animal. There are no if's, but's or maybe's. The correct action is a quick euthanase, by crushing the skull on the spot. This IS humane... forget laws, paperwork and the fact that the owner of the culprit dog is in attendance.
Too many 'wildlife' carers are to soft when it gets down to the bare bones.
In the snakes world...the world of nature... the world that our 'wildlife' lives in, things are far from rosy, and all carers need to get an understanding of this fact. Not just a trendy, superficial ideal... but a proper understanding about your role in helping the animals, and when the help boils down to relief from misery then LEARN to do the right thing.
Even mentioning a vet here is ridiculous.
As mentioned earlier, the animal is a part of the environment, after euthanasing it PROPERLY by crushing the head, leave it there, in the bush. Then say your prayer. Job done.