First, as Ramesh Ponnuru points out, overturning Obamacare based on the current suit has zero votes that we can be reasonably confident about.
I would also note that there are at least four “no” votes we already know about. I don’t think there is any doubt about the three liberals on the court opposing striking it down. But there also should be no doubt about Roberts, who went through hoops to uphold Obamacare in 2012. In 2012, Roberts was concerned about disruption when the law had not even been implemented yet, whereas striking it down now would uproot the insurance arrangements of millions of people.
So, I think a fair state of play going in is that there are four definite no votes and that to win, the challengers will have to run the table with the rest of the justices.
On that front, Justice Brett Kavanaugh seems like an especially shaky vote, based on his opinion in one of the cases leading up to the 2012 Supreme Court decision (which arguably helped plant the seeds for the Roberts’ taxing decision).