With the entire Chinese mainland under their control, it took the PRC 22 years to be accepted as China, for the purposes of the UN and the permanent seat for China on the UNSC.
So, if the PRC didn’t control all of the mainland, what would happen? Imagine, for example, that they were able to secure Manchuria and maybe even North China, but the Nationalists still hold onto South China (one of the most common divisions in Chinese history). Would the the Republic of China retain their seat? Almost certainly. But there is almost certainly some point where the PRC controls just enough and is just useful enough as a counter against the Soviets that the West would recognize them as the legitimate government of China.
Assuming that point is not the historical status quo, what is it?
So, if the PRC didn’t control all of the mainland, what would happen? Imagine, for example, that they were able to secure Manchuria and maybe even North China, but the Nationalists still hold onto South China (one of the most common divisions in Chinese history). Would the the Republic of China retain their seat? Almost certainly. But there is almost certainly some point where the PRC controls just enough and is just useful enough as a counter against the Soviets that the West would recognize them as the legitimate government of China.
Assuming that point is not the historical status quo, what is it?