The thought experiment goes past everyone's point on gravity eventually creating a velocity that is devastating. What would such a mass (between 100 and 180 km in diameter based on map of Corsica) do if it just magically settled gently onto a land mass and then gravity came into play? It wouldn't be extinction level, but there are lots of regional effects to consider. Weather patterns would be a huge one. Continental plate deflection, which would affect ground stability and water flow. Certainly earthquakes if anywhere near even smaller fault lines. A change in Earth rotational speed and wobble.