If I'm deported, can I ever come back to Korea?

Possibly, but not immediately. Deportation is typically followed by an entry ban for a set period, which depends on the grounds and seriousness of the case. Some serious offenses may lead to much longer bans. After the ban expires, a future visa application will still be reviewed in light of your history. Preventing the deportation ground in the first place is far easier than undoing it later.