I think they could find another reason to strike it down. IMO, part of why the ACA was upheld is that it is (or was) a model that conservatives wanted to apply

I think they could find another reason to strike it down. IMO, part of why the ACA was upheld is that it is (or was) a model that conservatives wanted to apply when privatizing other government functions. (e.g. Social Security) Roberts in particular appears to believe in this sort of wonkish conservatism and it played well with liberals giving him some of the "above politics" veneer that has since been lost.