The way Palin explained it on Greta last night - the Massachusetts law is a states rights 10th Amendment issue. It wasn’t mandated on the entire country like obamacare. She actually articulated it very well when Greta asked her your same question.
I would expect an overturned fed mandate would cause obamunists to kick the states into adopting a system of uniform state mandates via federal bullying and federal support ala the old speed limit laws.
IOW states do it or else.