None of the more moderate democrats (manchin, etc) want to be the senator that overturns ACA as they will get primaried. Once its already overturned, there is very little risk of that occurring for further modifications. And even if they don’t, this bill is still the best one you are going to get until at least 2018 IF the Republicans pick up a LOT of seats next year.
I think you're dreaming on that. Manchin will run on the Medicaid cuts for West Virginia, the end of insurance premium subsidies, and the higher costs of premiums in general.