There’s no way the USA and/or nukes won’t get involved if Seoul is fully destroyed. Seoul and South Korea in general play a (somewhat) major part in the world economy, at least compared to the DPRK. There’s no way that the majority of the world’s countries who trade with the ROK will want them to fall to one of the most economically isolated countries in the world.
May I ask why you are seeking to leave? For your privacy and safety, tell me through private messages.