Scenario #1: The Repeal
They will repeal Obamacare even before the inauguration. They will rush to do it, they will not bother in the short run to implement a "replacement" (they will promise in vague terms that a replacement will be coming). There will be alarm amongst people who depend on Obamacare for their health insurance, but it will be ignored by the media. There will be joy and jubilation in the Tea Party; they will even bring out the Revolutionary War costumes and wigs again, and this will be all over the news.
President Trump will sign the Repeal into law in his first week as President.
The Repeal will also of course be "effective 2019," because no one wants to risk the consequences of actually doing this in the current Congressional Term.
They will promise to pass a new and improved version of the Affordable Care Act somewhere down the line. Sometime in 2017, they might actually do this, and call it, yes, "Trumpcare." It will be substantially the same as Obamacare, but it will be sold to Red States as a substantial improvement that is now based on "free market principles," not "government healthcare." No one will notice or remember that actually the Obamacare exchanges constituted a patchwork free market solution.
Meanwhile, the Democrats will be in complete disarray. Every complaint from Democratic politicians will be dismissed with a Tweet or two from President Trump.
All of this will be so outrageous to former President Barack Obama that he will come out of retirement in 2018, and declare that he's running for a third term as President.