The test, predictably, failed, and this is probably why China was not as worried as they could be. Getting rid of Kim Jong Un is not a particularly high priority as a rabid buffer state is still a buffer state unless those claws get too sharp. A friend of mine sees this as another sign of US decline, but while the US power projection is declining, it also remains true that a rival hegemonic power doesn't emerge because the candidates aren't there. China is powerful, but has a severely slowed economy (although still faster than the developed ones, but people who know anything about growth patterns in economics shouldn't be surprised by that), Russia has a GDP of Italy and while it does have some serious ordinance, its ambitions seem to be purely regional to Eastern Europe despite a lot of the bluster. It hits harder militarily than its economy lets on, make no mistake, but Putin's concerns are limited to limiting NATO and keeping a Sunni block developing towards his Southern border. Europe leaders is a major power but still sees its bread buttered mostly in sync with the US even if individual countries oppose specific military action. BRICS never could correlate around united interests because honestly they don't clearly have united interests.
Always, but particularly now, the basics of political life and geo-political life are practical.
So, like the Roman Empire after the 3rd century, that decline may go awhile without anything really emerging to rival it. Furthermore, my normal response applies: capitalism does loom.
So South Koreans aren't freak out just like I learned not to while I was there, but there are concerns. The likelihood of cyberwar being the reason for failure is really low. In event of a war, Russian and DPRK both use those older methods because they are less hackable. They would, however, still almost instantly lose in such a missal war but only after doing massive damage Japan or Hawai. This is a bargaining table and there is very little the US can do unless it wants to use an ICBM itself. This puts South Korea and Japan in a shit situation, but Japan wants to re-militarize and has the technology now.
A lot of the future of the ROK depends on the the upcoming election, now that daughter of the former dictator and really weirdly scandal ridden Park administration is over, it's time for a change. A change that is willing to do some complicated negotiations between China, Japan, and the US. Moon Jae-in make be able to return Korea's Democratic party to same status after the Roh Moo-hyun's suicide and the collapse of the Sunshine policy. Conservatives in Korea have been split between Protestants, represented by Lee Myung-bak and the Grand National Party and Buddhists represented by Park Geun-hye and Liberty Korea (which split from Lee's Grand National Party), although it's important to know that Park was completely secular with cultural ties to Buddhists and Catholics (like Roh Moo-hyun actually). Lee was seen as Korea's slightly more moderate George Bush whereas there is little US analogue to Park (although maybe Trump in time).
Given that Japan is scrambling jets now to deal with China, not the DPRK, things are about to get complicated.