it's just same as your language. Online chatting is just same as your real life term as well, even it can be changed a bit thou. And before I explain, we have to know there are many ways for Corean language expression like very formal(such as in business or for older people, etc), formal, informal and very informal. In here, I will show examples which are formal and informal. Because we usually chat with friends or aquaintance or people who are similar aged. But if you do need formal term, you can send me an memo with your question. Well. Ok, let us think in English. When actually neither of us really there(=both leaving) or leaving(=both staying), what do we say in English? Probably we might say before say good bye to friend from online '- It was fun(재밌었어요-formal, 재밌었어-informal)' and then we can say like following: 1. Both leaving 둘다 떠날 때 - Bye(you can say 안녕히 가세요 but probably for chatting we can use more often '잘 가요' which means same. In direct meaning of these is 'I hope you will go safely' but we just mean 'good bye' with this term. In this case you don't use 안녕히 계세요 or 잘 있어요 because these mean 'I hope you will stay safely which we say these when there will be someone who will stay online. - Night(if it's around time to go to bed)/Have a sweet dream. - 잘 자요(formal), 잘 자(informal)/좋은 꿈 꾸세요. 좋은 꿈 꿔. 2. Both staying 둘다 머물 때-It can be awkward to say nothing so we usually say in Eng at this case like following - It was nice talking to you(재밌었어요, 즐거웠어요- formal. 재밌었어. 즐거웠어-informal) and we can probably use like following. - See you later, See you around(다음에 봐요-formal, 다음에 봐=informal and between friends who are similar ages), See you again(또 봐요, 다시 봐요- formal, 또 봐, 다음에 봐 - informal) - Talk to you later(다음에 또 얘기해요- formal, 다음에 또 얘기하자-informal) But as we all know in English we can use those above terms, No.2 in both cases, when we are leaving or staying in either way. Are they clear enough to understand? I hope it could help you somehow. :) 다음에 봐요, 모두들.

just "안녕 "ok!

안녕히 계세요 - u would use this when u are leaving while the person that u are talking to is staying. 안녕히 가세요 - u would use this when u are staying while the person that u are talking to is leaving. lol when I was young I got confused too. and my mom would always try to fix what I was saying. so just know that it's not only u who gets confused. even koreans like myself gets confused too. ;P

you can use those expression. 다음에봐요~(see you next time) / 나중에 봐요~(see you later) 안녕~(bye)