Probably the same thing we did when agriculture went from 70% of the workforce to under 1.5%. People will adapt to fill new demands.

If it comes to pass at some future time that machines can do all the work and everyone can live a Garden of Eden existence, goods and services will be so cheap due to their natural abundance, that UBI might be feasible but food and essentials might be almost not worth the trouble of metering.

We’re really, really far from that being a reality or concern, IMO.