Nothing will happen, North Korea likes to make these threats in a vain attempt to keep relevant and in the spotlight, the UN will still discuss their sanctions against North Korea and then impose them (then the North concedes concessions to release the sanctions only to start building missiles again... rinse and repeat).
If they do attempt anything on the 11th, it will be purely symbolic in nature, the North can not have attempt to win a war which lasts even months... Seoul however is relatively close to the border, if they attempted to capture Seoul from the South and then offered an immediate ceasefire in exchange for considerable concessions... I could see logic in attempting to do that (sort of similar to the Schlieffen Plan by Germany in WW1).







