Ultimately, a similar fate that happened to Celebration. Disney would immediately realize that they didn't want average citizens being able to vote for regulations regarding the company's land, they didn't like managing a police force and a court system.
Most of the companies that initially sponsored the "City of Tomorrow" would either file bankruptcy, be acquired or move on after the initial 10 year sponsorship. Disney would be left with a bunch of aging 70's style homes surrounding an enormous office tower they couldn't lease out space within.
The monorail system may have gotten built as a form of mass transit, but I don't believe the People Movers would have.
In short, we end up where we are today except instead of de-annexing Celebration they would have evicted everyone out of Progress City, as that land is prime.
That's assuming the entire company didn't go bankrupt trying to build Walt's vision.