Vacuum energy extraction: What happens to the cosmological constant? If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same? .  
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If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same?

A cosmological constant is one possible description of how dark energy behaves. We don't know the equation of state of dark energy for sure, but current data do seem to be consistent with the hypothesis that it behaves as a cosmological constant, which is also the simplest hypothesis mathematically.
A cosmological constant is constant, and therefore it can't be extracted in the sense of lowering the amount of dark energy in a given cubic meter of space and transforming it into some other, useful form of energy. There are various kooks who claim to have promising ideas about how to do this, the most prominent probably being Myron Evans. They are kooks.
Regardless of the equation of state, general relativity has local conservation of mass-energy (technically expressed by the fact that GR is not self-consistent unless the divergence of the stress-energy tensor is zero). This implies that you can't just locally increase some form of energy (e.g., by doing mechanical work) without decreasing some other form of energy (e.g., dark energy).
On a cosmological scale, it is certainly true in some sense that dark energy causes other forms of energy to appear. It drives the accelerating expansion of the universe, which can be thought of as involving large amounts of kinetic energy. The reason for the qualifiers like "in some sense" and "can be thought of as" is that general relativity doesn't have a global law of conservation of energy that applies to cosmological spacetimes. In fact, there is not even any satisfactory way of defining the total energy of a region of the universe that spans cosmological distances. (The technical statement is that we don't have a measure of mass-energy that is conserved and transforms as a tensor.)
