Speaking of China, it is using North Korea as a buffer between it and the West. The UN Refugee Convention was originally drafted in 1951, with a 1967 Protocol. China signed both in 1982. China signed the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment in 1987. These treaties expressly forbid the deportation of refugees back to a country where they will be tortured, imprisoned, and executed, which is exactly what happens to North Koreans when they are returned to the DPRK. Both treaties were signed well after China replaced the ROC in the UN in 1971, so China cannot claim that it inherited conditions of which it was unaware.
Given the high-ranking position of the defector, we can be sure Kim Jong-un was enraged and sought reprisals against his family using the long-standing tradition of his father and grandfather, Kim Jong-il and Kim Il-sung, respectively. We know this because of what happened to Hwang Jang-yop's family.
Hwang had been chairman of North Korea's Supreme People's Assembly, president of Kim Il-sung University, in charge of international affairs for the Workers' Party, and the creator of the DPRK's national theory of self-reliance, juche. Hwang had also been an advocate of Chinese-style reforms, allowing capitalism with the government still in firm control. He was not the only one with this philosophy, as Kim Jong-un's uncle, Jang Song-thaek, who was executed in 2013, also felt this way. But then he defected to the ROK.
500 of Hwang's family members and acquaintances were sent to the DPRK's labor camps, with a number of them committing suicide, including his wife and at least one of his children, because they understood their fate only too well, with the philosophy of songbun guaranteeing that even their children would be punished. Distant cousins of Hwang who did not know they were related only found out when they were arrested. The arrestees included a child who was asking for candy from his grandfather at the time of the arrest
Kim Jong-il, the leader at the time, sent two North Korean majors into South Korea to execute Hwang, with them posing as defectors. They were discovered before they could complete their mission and were imprisoned in South Korea.
Given that Kim Jong-un is more ruthless than his father -- Kim Jong-il only placed his brother-in-law Jang under arrest, but Kim 3.0 had him publicly arrested and killed -- perhaps the number of family members and acquaintances in this latest episode exceeds 500. We may never know.