Is it really paranoid ? USA, South Korea and Japan would like a regime change, but probability of committing their own armed forces to that goal is very low these days. China is quite a different story. They are already deeply involved in North Korea, which depends on them in many ways.

US should worry about its own weak leader elected (presumably). Peace as the Chinese say is unlikely. Everybody and his brother will work to exploit the situation. Wars May breakout. There is always somebody like Osama Bin Laden waiting to inflict a damage on America when a weak president like Bush (jr) got elected.