Based on my common sense as a native speaker, I would say it is quite awkward to say 내려가세요 even when the elevator is going down. And I'll say '들어가세요' when I have to say goodbye, because they are mostly on their way to one's home. If it isn't, which means it's morning so everyone is leaving home, I can say 안녕히 가세요.
So 안녕히 가세요/계세요 also makes sense, by the way....
You have to say "안녕히 가세요" to the ones leaving a place as well.
The followings are different ways to say goodbye in Korean:
안녕 (informal). (Well-being, peace, health.)
안녕히 계세요. (Stay in peace.)
안녕히 가세요. (Go in peace.)
잘 있어 (informal). (Stay well.)
잘 가요 or 잘 가 (informal). (Go well.)
나 먼저 가 (informal). (I will go first.)
다음에 봐 (informal). (see you next time.)...
As a Korean, I can translate it into English like this:
You can just respond "안녕하세요", but "네~ 안녕하세요" sounds more friendly and is used more often.
In this expression, '네' is basically used to respond affirmatively (positively) to someone. (polite form)
It has a emotional meaning - to tell someone that you are hearing affirmatively, and ...
Well, if you are at home and your parents (or some other 어른) are back home, you say "안녕히 다녀오셨어요." But (I think) English speakers don't say "welcome back" in such a case, so it's kinda different.
Other than that, I don't think Korean has a good analogue for "welcome back". I think the usual expressions for "welcome" are used instead: "어서 와", "어서 오세요", or "...
If you want to mean "welcome" in Korean, you should write it like "환영합니다.", rather than "환영".
"back" means many different way in Korean, you should express exactly "returning".
"returning" is form of -ing(~하는 것), and "return" is "돌아오다".so, returning is "돌아오는 것"
so, "welcome back" is more natural in "돌아온(돌아오는) 것을 환영합니다."
'안녕합니다' means 'I am well'. It's not grammatically incorrect.
However, as a response to '안녕하세요?', it can be perceived as a joke or even an insult.
It's analogous replying to "How do you do?" with "I do well."
It implies that the person is returning home (literally go into their house).
Etymology is vague but I've heard of two origins:
One from people meeting outside, in a coffee shop for example, and then when they part, they say they're returning home.
Another is from the old days when there were no home phones. You had to use public payphone to make a call ...
There are a couple of ways to say this, depending on who you're talking to and the level of familiarity with them!
밥은? = Food? (did you eat?)
밥 먹었어? = Did you eat (food)?
점심 먹었어? = Did you eat lunch?
점심 먹었어요? = Did you eat lunch? (to unfamiliar people)
점심 드셨나요? = Did you eat lunch? (to older people/unfamiliar people) but
using '나' ...
So, here is my first draft. Something may be omitted or altered.
먼 거리에도 불구하고 여러분의 소중한 시간을 들여 저희 아이들의 결혼식에 참여하시어 자리를 빛내주셔서 감사합니다. 맛있게 드시고, 즐거운 시간 보내시기 바랍니다. 다시 한번 진심으로 감사드립니다.
(assume wishing you delicious mean enjoy your meal or something like it.)
양가 대표님께 다시 한번 감사인사 드립니다. 양가 대표님은 다시 연회장으로 돌아가 하객 분들과 함께하시길 바랍니다.
(So this might be wrong. celebrate ...
If you have been waiting for the listener who is one or more of your close friends around your age, you can say "잘 돌아왔어!" or use a rhetorical question "돌아왔어?" (or "돌아왔니?", "왔니?", or "왔어?")
If you did not know that the listener would come back, you can say "돌아왔구나!" or "(난 네가) 돌아올 줄 몰랐어!"
As a hello (when meeting someone), '안녕하세요?' means something like 'are you getting on peacefully?', - possibly not so far away from 'how are you?' in English. As in English, you don't have to interpret it literally as a question that needs a reply, but you can do so - so just saying '안녕하세요?' - 'How are you'? is fine, or '네, 안녕하세요?' - 'Yes, I'm doing fine, ...