Uh yeah, it's おはようございます – happens to the best.

Don't know how much おやすみ applies to "Good night" as in "Good night, Vienna" and such.
Thinking about it in German it makes sense, too, as in a good bye, even though the primary use of German good night is "You're going to bed? Good night" (which sort of is what the German "Good night, Vienna" leads to, too – don't know whether it's the same thing, or different things in English).
I have never heard おやすみ as "Good bye, have a good night, whatever you'll be doing in it" in Japanese (or any other language) though.

_{Snarky comment: Good bye isn't a greeting though, is it?}