In terms of appointments, republicans have had control of the Supreme Court for years. In terms of the actual judges and their rulings that’s anybody’s guess. They could easily remove the tax while keeping the rest of the law unchanged or do just about anything.

I don't really know what to make of "republicans have had control of the Supreme Court for years." Overturning Obamacare was their number one priority during the Obama administration. The Supreme Court chose not to. The five justices who chose not to are still seated. Some control.

Scalia and Kennedy where both republican appointments and replaced with Republican appointments. So if you’re saying they have 5-4 control now they also had 5-4 control then.

https://en.wikipedia.org/wiki/List_of_justices_of_the_Suprem...

That said, many justices have not voted as expected. In other cases political parties have swapped positions on various issues etc.

  the 5-4 majority that saved Obamacare last time will not survive a few more Republican appointments

You seem unaware that Chief Justice Roberts authored the opinion upholding ACA.

So what? The Chief Justice can write the minority opinion next time. That 5-seat majority includes some who will almost certainly retire in the next four years.