N Korea IS it's ruling elite. Very few of them would survive, or be allowed their freedom in such a case. Hardly a retirement fallback.
I agree, and that was exactly my point when I mentioned:
"I expect Kim's main goal is to stay in power, and if possible expand that power."
That last point may have truth, but I don't think it's applicable in this case.
Well, I believe the thing China wants most is to regain Taiwan. Two things making that goal much harder to obtain are an increased US military presence in East-Asia and poor US-Chinese relations. And both of them will be caused by China avidly supporting North Korea.
I don't think China wants to rattle the US' cage just for the sake of rattling. If they do, I expect there's a purpose behind it.
As to China, I think the issue was larger than having a US "puppet" on their border, which was communist slang for democracy. Surely you use the word ally rather than puppet, do you not?
Finland was a real democracy on the border of the Soviet Union, yet they were not considered a US puppet by anyone. So it takes a little more than only democracy to be considered a puppet.
http://en.wikipedia.org/wiki/Puppet_government
"A puppet government is a government that, though notionally of the same culture as the governed people, owes its existence (or other major debt) to being installed, supported or controlled by a more powerful entity, typically a foreign power. Such a government is also known as a puppet régime."
Many in South Korea perceive their military security to be dependent on the US, and their economic growth on generous trade agreements. Thus they owe a fairly major debt to the US.
We could argue about ally/puppet status until the cows come home. Would you instead simply agree that South Korean foreign policy towards its neighbours is far more influenced by US foreign policy towards those same countries than the other way around?