Taking our ball and going home is not a great military strategy unless you're sipping espresso on the Champs-Elysees. Theoretically, the Japanese could tell us the same thing. And then we'd have no presence whatsoever in the region if we employ your strategy.
We don't need to react like a bunch of hillbillies because the leader of South Korea is senile. We'll never have a military base this close to China again. To leave would be a disaster.
The token troop presence we have there contributes very little to the actual defense of Korea. They are tripwire troops, which guarantee our involvement should the balloon go up. It is very similar to our former presence in Berlin before the wall came down.
What good is this military base beyond its symbolic presence? The Chinese could take it out in a heartbeat if an actual conflict broke out. Carter denuclearized the peninsula a long time ago. In terms of intelligence, our satellites and other assets can do just as well as a land base.
South Korea has a modern, well equipped military more than capable of taking on the North. The South has 48 million people versus 23 million people in the North. By every measure, the South has the resources and wherewithal to defend itself against the North. The US can supply the nuclear umbrella.
It has been over 50 years since the end of the Korean War. South Korea has the 13th largest economy in the world, larger than Australia, Russia, Switzerland, Poland, Sweden, South Africa, etc. North Korea is one of the poorest countries on earth. It is time to cut South Korea off of security welfare and set them free to fly on their own.
We used to have military bases in Taiwan during the Vietnam era.
What with the heightened tensions between China and Taiwan, I'm relatively sure that if we asked Taiwan for some land to build US military bases, they'd be more than happy to oblige.
Which would get us US military bases ON Chinese soil.
(It'd also oblige us to defend Taiwan, instead of cutting and running like some in Congress would want us to do.)
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As for pulling out of South Korea.
The South Korean government is currently (and for the foreseeable future) only authorizing the US troops in South Korea for the defense of South Korea in case of NK aggression.
The only way we were allowed to pull some troops in South Korea out for Iraq was by having them permenantly removed from the Korean peninsula. (Which is why you saw that there are now fewer US troops in South Korea.)
This means that any US troops stationed in South Korea are useless for dealing with any other problem that might arise worldwide.
Which isn't all that good of a deal for the US, is it?
Why should we keep 32,000 of our troops in, for all essential purposes, a 'lockdown'? In a country that does not want us there? That proclaims to control how the US can use it's military regarding North Korea?
No, it would be better to reposition our troops to Japan. Then enforce a 'scorched earth' policy in regards to a possible North Korean invasion. That if North Korea invades the South, that we would destroy all the factories, all the powerplants, all the ports, all the dams, and all the roads of Korea.
Let's see North Korea build anything after that. (Not to mention the huge boost to the Japanese economy that would result from the sudden absence of Korean cars, electronics, cellphones.)
And we'd still have our troops in the area, should we wish to move back into Korea.
And we'd have 32,000 move US troops that could be used wherever the Pentagon thinks that they are needed.