In practice, libertarianism kinda eventually leads to neoliberal democracies. Look at the original government of the United States, the Articles of Confederation (roughly 1777-1789). It was designed by a bunch of land-holding, slave-owning southern plantation guys and goods trading, finance northern dudes to be the most minimalist, pro "individual" (ie pro entrenched wealth) government ever seen. It was a joke and fell flat on it's face. They had to get back together and put together the proto-liberal framework the US is still running on. When given real-world authority, libertarians eventually have to ask questions like, "Who oversees contract disputes? Who negotiates with other nations? And how do we pay them?" and their solution always ends up being a recreation of liberalism from first principals libertarian ideals.

I'm not sure what you mean by neoliberal social democracy. These are two very different form of capitalist ideology, and one result of the transition from social democracy to neoliberalism in Europe over the past few decades is pretty much what you're writing about in regards to libertarianism: proletarianization of what was previously comfortable "middle class" people, combined with even further marginalisation of poorer workers.