Complex sentence: The advent in the late 1990's of CAD see's the partial demise of the technical drawing pen but Rotring diversify into a wide range of graphic pens, pencils and markers.
Split into simpler sentences: The advent in the late 1990's of CAD saw the partial demise of the technical drawing pen. To combat this, Rotring diversified into a wide range of graphic pens, pencils and markers.