This always seems like a question with an agenda.

What happens? Well I suppose the economy collapses and the proletariat rise up and usurp power, or something fantastical.

What’ll more likely happen is we’ll further automate repetitive low skill tasks, and / or start making more durable goods, or otherwise ingenuity our way forward.

Post-industrialized countries make it impossible to for those countries arriving late to the party to advance any further, by way of global environmental agreements and glass bead "carbon credit" payments, thereby ensuring a permanent pool of slave labor.

Eventually it becomes more profitable to automate. See: Sony's automated PS4/5 factory. Formerly these would've been assembled in some Foxconn plant by tens of thousands of low wage workers.

I have a sneaking suspicion that's fundamentally impossible, as some of the prerequisites for developed economies (in the modern, not-industrialization sense) seem to require predatory exploitation of developing economies. And the global inequality of capital ensures there's a power disparity sufficient to enforce it for the former, to the detriment of the latter.

But I guess it's really a question about post-scarcity economics, and whether they're possible?

It happens very gradually, and in aggregate we tend to end up working fewer and fewer hours per year.