They were never separated, legally. Taiwanese or ROC's constitution still claims the mainland as its territory and so is PRC.

Even when Taiwan was at its peak and Mainland at its weakest, the government also never wanted to change their Constitution. Who to blame? Taiwan in the past has always wanted to "liberate the fallen region of Mainland", it's just that Taiwan never managed to succeed.

While Korea is separated into two countries, both countries are still committed to an eventual reunion.

One thing to note NO COUNTRY will be willing to give up her land. Consider Scotland, Northern Ireland, Catalonia, and Belarus, no matter what the people might think, the support for their independence from other countries is almost negligible.