Scalia is the key. He ruled for the unions in a similar case back in the early 90’s.
I don’t believe Scalia would have been for defining people as “public employees” for some purposes when they don’t qualify for any of the benefits that come from being a public employee.
I could see this case being decided very narrowly on those grounds, without actually getting rid of public unions or their forced dues.
Most people think the forced dues is the issue, but I think the court could simply rule on the definition of an “employee” instead.
That would be the easiest way to drag Scalia to the majority, if he otherwise was going to side with the union.
If Alito is writing the opinion (and circumstantial evidence suggests so since he hasn’t written any yet) it should be bad for the union at least partly, because Alito seemed clearly for the plaintiffs in the case. He wouldn’t get Hobby Lobby because it is too big a case, Roberts would want that one.