Your scenario would be absolutely historic. The Democratic front-runner pulls out, and a third party non-politician wins the election. Sorry, I just don’t see all of that happening.
As for the idea of a third party non-politician? First of all, how do you just assume it will be a non-politician. It could well be a disenchanted Democrat or Republican. But with the general and growing contempt for the Washington crowd, a non-politician might well have the advantage.
Ross Perot, of course, was what you describe, and even with his inability to use the television address, correctly, was on the verge of making it a roughly equal three way race in 1992, before he had a paranoid incident, pulled out, and then reentered. He still got 19% of the vote, however.
Someone who understands how to use the TV address, as FDR--forget for the moment the wrong-headed policies--used the radio fire-side address--might win by a landslide.