Questioning by justices is a rather unreliable guide as to how they will vote.
Questioning plus their previous decisions can be pretty reliable.
Also in high profile/political cases, the questioning tends to be more indicative of positions.
Kav seems to be a severability guy, which is a solid approach.
Roberts already saved the ACA before.
Knock off 2 conservative votes and the ACA is safe.
Otherwise, I think there's just no appetite to kill off ACA now.
The timing right after a new president was elected is poor.
Plus the pandemic is the ugliest time to rip insurance away from 23M.
And ACA has run for a decade now, and is part of the landscape.
Roberts is very mindful of the court's prestige and institutional role.
And with three fairly new justices, I think Roberts will be able to hold sway over them. Really all he needs is to persuade one other conservative to join him.
Not to mention that the case is fairly weak in itself. It's more like a legal exercise rather than a genuine case. Which is where standing comes in. Often when the court wants to punt and not decide, they bring up standing issues, and the conservatives of fond of denying standing to individual plaintiffs, believing the courts shouldn't decide too much. I don't think it would be hard to rustle up 5+ votes for lack of standing, allowing the premise of the case to linger without deciding any merits.