I'm not a native speaker but I think I can help you. 안녕 is used as the "hello" or "goodbye" in Korean. In Hanja, or the Chinese character counterpart of it, it has another meaning. 安寧 is the Hanja counterpart of it and it has the meaning of peace, safety, or tranquility (same for Chinese and Japanese). The 안녕하세요 expression came from the word 안녕하다 which means to be well, so they say it when they leave. But as the time goes by, the use of Hanja gradually declined due to the use of Hangul. So the meaning of it became vague/ambiguous and as a consequence, some Koreans does not know the real meaning or the root word of modern vocabulary. So, I could say the meaning of it became obsolete since they have another term for peace which is 평화/平和 (same for Chinese and Japanese). Nevertheless, if you want to use 안녕 as peace, use 安寧 instead.