if you thought the disney ending was sad (spoilers)
in the book, tod finds and mate and has a litter, and the hunter kills his mate and babies, and then it happens AGAIN, tod dies from old age and exhaustion of outrunning the hunter, and copper gets shot. and the roles of copper and the chief are reversed, so little puppy chief gets hit by the train and dies. how depressing.
[Everybody's happy nowadays]