I wrote a 101 Dalmatians retelling, and as far as I know from the research I have done, 101 Dalmatians is not yet part of the public domain. But my retelling is almost completely different from the original; the only similarities are the names and the fact that I make a few references to the original story and how it's generally told. But the roles of the characters have been switched and the point of the retelling is to show it from a different perspective. The narrator states that the way the story has been told is completely wrong, but even when referencing the original, I don't use the title of the book. Does it seem different enough for me to publish? Sorry if this is lacking information, but I'm trying to be as ambiguous about the story as I can while still giving necessary info for an answer...
In general, fictional characters are copyright protected. You can't publish a story where Cruella De Vil opens an animal shelter, for example. It doesn't really matter what the work is about, you can't take someone else's well-defined creation of the character's name, description, and demeanor, and use it as your own. You would be leveraging someone else's intellectual property to publicize your own work.
People retell stories all the time. The question is, are you retelling the story, or reusing the world? You generally can't reuse the world (although there are cases that have been successful, like Alice Randall's The Wind Done Gone). But there's little that can stop you from retelling the story.
Note that the history of The Wind Done Gone is very relevant to you as you seem to be reusing someone else's world rather than just retelling the story. People do get finicky about that.
And if you really want some fun, see the pedigree of modern stories like The Terminator in answers to a question of mine over at SciFi.SE.
The one thing you should have going for you is your retelling is original in that people could recognize its antecedents, but the story stands completely on its own.
The one thing really against you starts with a statement my retired attorney father was fond of saying: anyone can sue for anything at any time. You could have picked an easier antecedent. Disney is very big with a lot of laywers... and they tend to fight for what they perceive is their property.
Which would be more than hypocritical since pretty much every story/movie they've ever made was a retelling of another story. Take, for convenient example, 101 Dalmatians, which was a movie based on the book One Hundred and One Dalmatians by Dodie Smith.
I wonder who actually has the copyright to the original story?