"Nos vamos" means "were leaving", so I say that with the children I watch when its time to leave the house. "Come on, put the dog doen, were leaving!" Or you could say this at the end of a conversation, "We're leaving now, but it was nice talking to you!"
I think you may be thinking of "nos vemos", which means "we'll see each other". You can definitley say "Adios, nos vemos!" More or less meaning "bye, see you later!"