Never heard this expression tbh, where is it used? The UK maybe?

I have never heard that phrase used and im over 50.

I have never heard of this before so I guess it already happened?

The save icon still tends to be a floppy disk, so I'd say you have a while yet

Probably a while. People still say "roll up the window" even though most haven't "rolled" up for close to 10-20 years now.

Probably two or three generations after those who actually handled pennies, but then again it wouldn't be the first time an old phrase or usage fossilised and remained in a language long after its full meaning has been obscured by time.

One example that springs to mind is the "ut" of "utmost". It's an old spelling of "out", but the word has stuck around because "out(er)most" means something else.

The UK still makes pennies.

It already happened

How long did it take before references to ha’penny (pronounced haypenny, short for half penny) stopped after those were phased out?

There’s a song I know of that mentions them and that’s it. They were in use starting in 1672 and phased out in the 1970s, so a hugely long time, yet they are never mentioned anymore despite being in use during modern lifetimes.

Perhaps people from the UK hear the word more often, but I basically never come across it in media or anything, even period pieces.

(The song I know is “Christmas is coming, the goose is getting fat, please to put a penny in an old man’s hat. If you haven’t got a penny, a ha’penny will do, if you haven’t got a ha’penny, than god bless you”)