The primary goal of the NK regime is survival, not suicide. The latter is just MSM propaganda that justifies US public acceptance for weapons programs that reap billions of profits to the US military industrial complex. 

The US has attempted regime change over 40 times since WW2 (remember Viet-Nam as one notorious example?). NK is just one of the targets of US regime change for those who don't kowtow to it. Other than that, the US doesn't mind despotic regimes (including head chopping ones like Saudi Arabia), as long as they are under its influence and control and they buy lots of US weapons.