Dowun holding Hong Lyon's hand while she was unconscious made my heart cry. He has always been the calculating type, the one who never does anything on a whim. Him holding her wasn't necessary for his plan at all. She may have grown on him more than he could fully admit.
He and his dad may have latched on to her as their golden ticket, and this arc showing Hong's illness suggests a tragic end, but I predict Dowun never leaving her until the end... even if it meant leaving power, the one thing he built his whole life on, behind.