Oh no, i'm so scurred!
Do you actually believe they have the capability to follow through?
Why would we care about Nork threats of total destruction? They make them every year.
In any case North Korea is welcome to try,
but that will also leave a huge crisis on China's border, namely refugees, along with US troops and a solidly pro American and possibly anti-Chinese South Korea.
It does force the South Koreans into considering you, but I wouldn't say that coercion sets the basis for positive political relations in the future.
As you say, it is acceptable to China for security reasons, that said I say its fundamentally flawed because US troops on China's borders are not a big threat in the first place.
Just consider the size of China, the US has no interest in invading that, what do you think we are Imperial Japan? We already have our continental power, there is absolutely no benefit in invading China.
This was a definite concern in the cold war, but now i'd say it's outdated and China should focus on how it can best unify the Korean peninsula under favorable conditions to facilitate and give reason for a US drawdown and for South Korea to view it favorably.
That would be very interesting.. what would the effect of all those north koreans be on Korean politics... well that's a moot point now.