Rikki Tikki Tavi was a weasel vs cobra and not a constrictor. I would venture to bet that a good strike and wrap would result in a dead mammal. I would not take a chance but I really don't see this as a categorically implausible outcome. I don't know how much nutrition a snake would get out of a ferret but they do seem to be shaped like ideal snake food for a large enough constrictor.