How to deal with the world’s most dangerous regime

I cannot understand that in intercontinental ballistic missile era, why the North Korea still has the strategic value as a”buffer” to Beijing. It might be used as a bargain chip but no more a buffer?

http://www.economist.com/news/leaders/21721146-donald-trump-grapples-his-trickiest-task-how-deal-worlds-most-dangerous-regime