Damage to trunk
Our dog almost chewed through the trunk of a young plum tree that we recently planted. Can it be saved? Can we get it down to the original "nub" which is approx 2" from the ground so it will grow again or should we just dig it up and start over?
It looks like the dog has chewed off the bark down to about 1" above the graft union (the nub you referred to.) You could try pruning down to that part of the trunk which has bark remaining around the entire circumference. If it sends up a strong sprout from that scion wood (the good plum variety) above the graft, you will get the plum variety you want. However, any sprouts from below the graft will be a different variety selected for cold and disease tolerance and not the fruit quality. It may be difficult to tell what you're getting.
Unless you want to take that slim chance of success, we'd recommend replanting in the spring. Use a cylinder of wire mesh, such as hardware cloth, or a plastic expendable spiral to protect the bark from your dog. And maybe a few more toys to entertain the dog?