It depends on which factor it crashes down to 200 dollars. If it is from the bitcoin protocol failure which is highly unlikely I believe I would not sell or buy but would sit on the fence and watch the developments. If it is from a market price crash I would buy all the money I have in bitcoin and hold them, I missed the boat in January 2015 when price was even below the 200 dollars mark so I don't want to miss another boat if it happens again.