Yes libertarians advocate doing away with all federal programs except as needed for national defense and foreign policy. But that doesn't mean the states can't take over the federal programs that they want. Its just that its unconstitutional for the feds to do it. So SSI could be handed over to the states to handle. It just makes all these programs a little easier to control on the state level.
I have nothing against universal healthcare but it should be up to the states to try different methods. Maybe they could find a system that actually works.