It's said that 「さよなら」 can be used when you are parting with someone that you do not expect to meet again, hence the song name 「さよならは言わない」, etc.
However, it's also not rare that 「さよなら」 is used when you do expect to meet someone again, perhaps as a more polite form of 「では」 or 「じゃ」?
And it seems that you can even respond to 「また明日」 from a classmate with 「さよなら」, and of course not to mean "no, I do not want to see you again".
It's also used by a podcaster saying goodbye to his listeners at the end of an episode, again of course not to mean "sorry this is our last episode":
勝手にEnglish Journal (14:02)
So here comes the questions:
If 「さよ（う）なら」 can be used both when you expect and do not expect to meet someone again, how can the listener know with which meaning you are using it?
It seems to me that 「さよ（う）なら」 is used much more often as a daily parting phrase in some old Japanese films, e.g. those by Ozu Yasujirō. Is 「さよ（う）なら」 nowadays less often used as a daily parting phrase but more as a sign of (voluntary) permanent parting?