Thongil is what you become after seeing Kim Jong-Un in a bathing suit.
I don't think China would allow a non-Communist regime allied to the US on its border although they might accept a less-extreme North Korea, maybe something on the order of Kadar's Hungary.
If someone like Obama had been President in 1950, the North Koreans would have succeeded in conquering the South. If they were to invade now, it would take Obama months to decide to do anything--it would be up to the South Koreans to defend themselves. The South Korean Army undoubtedly is more than a match for the North Korean Army, but what if the NK bombardment of Seoul has killed millions of civilians in the first day or two?