lol it isnt that simple...the world needs china, just as much as china needs the world...
plus...
CHINA must prevent north korea from getting demolished for 2 big reasons
1) the refugees will spill over china border, if war breaks out, china doesn't want to deal with all these refugees
2) Korea will be united under 1 government after north korea loses the war, (new gov will be pro american), having a completely pro american korea that has nuclear bombs and likes america , is not something that china wants across its border
3) china is the only country keeping north korea afloat they provide 50% of oil, and 80% of the north koreas food, and are the only trade partner... CHINA only doing this cause want to keep north korea afloat- elsewise the communist government will collapse!!