While the chaebols represent a huge part of the South Korean's GDP, they account for only a small part of the jobs in the country. Whether leaving them for another job is easy, that I don't know. Depending on the country's culture, leaving could also be very bad for future prospects.
Samsung has 0.1 million employees in SK out of a population of 52 million. It’s big, but that also makes it more difficult for them to replace people who quit.
Sure, but that’s at their current ultra low turnover rate.
If conditions are actually bad enough for people to be leaving it suddenly becomes much harder to recruit skilled people locally. Especially when there is news coverage of what’s happening.