The attitude is based on oral arguments in which all five conservatives asked skeptical questions, including the presumed “swing vote,” Anthony Kennedy, who seemed to see this as a basic question of liberty, the freedom not to participate in the market.
But here's my prediction, for what it is worth. The law will be upheld. Most likely, by a 6-3 vote.
The reason is basic. Without this law regulating insurance the government has no control over one-sixth of the economy, short of taking it over, which it is otherwise in the process of doing. The current law is a Republican solution, first proposed by Richard Nixon a generation ago, and implemented by Mitt Romney less than a decade ago.