Conventionally SK can take care of business. But what if, in a war, they decide to use nuclear capable missiles. Does South Korea have a good Air defence system?
That, indeed, is a risk of open war. However, i doubt the North Korean Leadership would be as suicidal to use strategic missiles on Seoul since a strike on Seoul would mean an imminent strike from the United States and other world powers. To do so would definitely condemn the North Korean Regime. Containing North Korea is a responsibility of the Chinese , who have a unique bilateral channel of communication with Kim Jung Un.