And “hasta nunca” would mean “see you never” and you would actually say it to the piece of bad trash. You wouldn’t say it to a friend. Even if you never expect to see them again, hey, I once ran into a High Schoolclassmate in NYC, some 12 years after HS graduation (we’re from a little town in Spain)
I’ve got to agree with mstay and others. Despite the theatrical meaning (“Is this really goodbye? Say it isn’t so!”), I’ve never heard “goodbye” in everyday language used to indicate finality. The shortened form, “g’bye,” is common here, often with another phrase after it, as in “g’bye, Wombat, see you tomorrow.”
Emphasis obviously makes a huge difference, and the word goodbye makes a strong command. Example:
Bill: Okay, Tom, Sue and I need to talk now.
(Tom doesn’t leave)
Sue: That means “talk without you,” Tom.
(Tom doesn’t leave)
Bill: GoodBYE, Tom.
Tom: (leaving) Well, if you’re going to be THAT way about it…
I read it the same as “a bientot”, “a demain” or “a la prochaine”, only without the space: “a dieu” → “adieu.” For non-francophonic anglophones, it would be roughly translated as “until [soon], [tomorrow], [the next time we meet] or [we meet in heaven].” Back translated into French, “until…” would be “jusqu’a [bientot] ou [dieu]” which would get you funny looks on the street.
…which brings me to The Secret to Speaking Foreign Languages: Don’t translate in your head as you speak. Speak only in the language you want to communicate in. The idioms will kill you.
Vlad/Igor
From Monty Python (not word for word though):
“Jenkins, at this stage of the war, we need a futile gesture.”
“Yessir.”
“I want you to fly over to Germany and not come back.” ( :eek: )
“Yessir. Understood, sir.”
“Good man. Carry on then.”
“Shall we say au revoir then sir?”
“No, Jenkins! Goodbye!”
“Take care (of yourself),” is usually used for permanent or long-term farewells.
You’re right. Propositions can have many meanings in different contexts. The french proposition a might mean at, or untill, or many other things.
but when I read the title, I could only think of this as a list of Canadian alternatives…
By the Clock on the Wall by Johnny Wayne and Frank Shuster…
Well I see by the clock on the wall. That it’s time to bid you one and all.
Goodbye (Goodbye) So long (So long) Farewell (Farewell) Adieu (Adieu)
Be good (Stay Well) Bye Bye (Keep Warm) Relax (And Eat) Take Care (Stay Loose)
Adieu mon vieux. A la prochaine. Goodbye 'til when we meet again!
That would explain the line in the old song… This is not adiós but just goodbye… Soon I’ll return"
‘Don’t let the door hit you where the good Lord split you.’ has an air of finality to it. 
Ah, yes, I think I’ve heard that before. My first thought was ‘à Dieu’ but then I went on to make the common mistake. Ah well, c’est la vie. 
I wouldn’t say that “goodbye” by itself has any finality to it, though it’s not often used in American English. Much more common is just “bye” (how one would usually end a phone call, for instance), or various other idioms (“later”, short for “see you later”, or “take care”, or any of various foreign loans come to mind).
However, context is everything. The phrase “this is goodbye” most certainly does imply finality, and could be used either in a “good riddance” sense, or as a Casablanca-style tearful farewell.
Which, come to think of it, is one case in modern English where “farewell” is the preferred term: When one is referring to the parting (and last communications before the parting) as a noun. One would seldom refer to a tearful goodbye, and never to a tearful bye, or a tearful so long or tearful see-you-later. Similarly, the last speech a politician makes on leaving office is his farewell adress.