I grew up listening to recordings of "Round the Horne" in the UK, which included two characters Julian & Sandy that chatted a little in Polari during their sketches. A bunch of Polari words and phrases have migrated into general UK slang — so it's not really a case of dying out… more migrating and changing — as languages & dialects often do.
I'm always astonished as to hows fresh Round the Horne sounds even today, when many of the comedy programmes of that era sound distinctly dated. Still funny, worth a listen.
As I'm sure you know but others might not, that's not a "real" Julian and Sandy sketch.
Edit: The classic Julian and Sandy sketches were recorded between 1965 and 1968. The last one was a reunion in 1987, shortly before Kenneth Williams' death.
I grew up listening to recordings of "Round the Horne" in the UK, which included two characters Julian & Sandy that chatted a little in Polari during their sketches. A bunch of Polari words and phrases have migrated into general UK slang — so it's not really a case of dying out… more migrating and changing — as languages & dialects often do.