Samsung is losing market share in China because of THAAD.

https://www.xda-developers.com/samsung-lose-market-share-china-q4-2017/

Samsung has lost its market share tremendously in China.  Samsung had a 20% market share at its peak but it would tumble to 1.6% in Q4 2017.  Besides the intense competition in China from other local mobile producers like Huawei, Xiaomi & Oppo, China citizens also stop buying Samsung mobile phones after South Korea began THAAD installation and all these affected Samsung sales in China greatly especially the boycott.

Any slowdown in China exports will impact South Korea economy because China is the largest trading partner for South Korea.  Furthermore, South Korea's economy is supported by its top 10 conglomerates in which Samsung contributes the most.  It is difficult for Samsung to make up for the loss in China market share elsewhere because China mobile players have also ventured overseas.

The only way to thaw the China-SK relationship is to remove THAAD from SK.