If the north escalated anything they would a) get their asses kicked back into the stone age and b) lose china's support. Their top fighter aircraft is the mig-29, which would be blown out of the sky by american f-22s before they even register on radar.
The last thing china wants now is a war at their doorstep, especially a potentially nuclear or chemical war. It's just the usual sabre rattling from the north because the world has forgotten about them.
