That's the real conundrum, isn't it? There's a reason why nothing has been done about North Korea yet.

North Korea holds South Korea hostage with their thousands of artillery batteries pointed at Seoul. China does not want a US proxy on their border. And the US does not want to get in war with China... especially a land war.

This has been North Korea's specialty for many decades: playing each side off against the other. North Korea used to be much richer than South Korea partly because they kept playing the Chinese off against the Soviets, and vice versa. Once the Soviets were gone, suddenly North Korea had a lot less leverage over the PRC, and that's where their serious economic troubles started.

Anyway, until the US and China are in agreement what to do about North Korea, nothing will happen to North Korea. And even if those two powers agree, Seoul will still be massively damaged by the opening salvo of any war.

Having said that, China is getting increasingly tired of North Korea's shit. North Korea is causing China problems, and don't forget it's a whole lot easier for North Korea to nuke Beijing than it is for it to nuke a US state (aka: nukes are bad news for everybody other than North Korea).