Is there a verb and analogous noun similar to ‘to greet’ and 'greeter' used when people depart?
Solution 1:
I don't think there is a suitable one word to use as a verb other than "bid farewell". Oxford Online Dictionary mentions that to farewell is used as a transitive verb in Australian and New Zealand English as in:
I farewelled my Scandinavian companions, and departed on a Kodiak boat with the Americans Judy, Hank and Cody.
For the noun, you could consider good-byer which means:
A person who is saying goodbye.
[Oxford Online Dictionary]
Solution 2:
It's not what you were looking for, but Sam can be described as the
host or doorman
host:
a person who receives or entertains guests at home or elsewhere: the host at a theater party.
a master of ceremonies, moderator, or interviewer for a television or radio program.
Emily Post says
Six Ways to Be a Good Host
6) Be appreciative. Thank people for coming as you bid them good-bye. And don’t forget to thank anyone who brought you a gift.
doorman: the door attendant of an apartment house, nightclub, etc., who acts as doorkeeper and may perform minor services for entering and departing residents or guests.
The verb is easier.
take leave
(Also, take one's leave of) Depart from, say good-bye to. Sorry but I have to take leave of you now. After the movie we'll take our leave of you. [Mid-1200s ]