Agree, its almost/already too late to do something about it. Specially because China didn't want to cooperate.
Zuid-Korea en VS waarschuwen Noord-Korea met eigen raketten | NOS
As expected again an exercise as revenge/warning to the North-Koreans.
There are only two 'solutions'.
1. Full scale war, try to wipe out most of their firepower with preemptive strikes and use the PAC-3/THAAD to intercept a part of their missiles and accept all collateral damage/civilian casualties.
2. Do nothing and tell the South-Koreans and Japanese that they have to develop their own nuclear arsenal.
Of course we can go for option 3.... Become good friends with Kim Yong Un. But that's quite unrealistic.