Eventually civilization would relocate to the oceans (where it's safer and more efficient).
Humans are descended from hunter/gatherers. Those two activities required large expanses of land so we were inextricably tied to it. Eventually humanity domesticated land and the required expanses became much smaller but they still performed hunting and gathering on it -- and called it farming. If food production could be completely industrialized to the point where there was no dependency on land at all, then the value of land for the sole purpose of habitation would diminish greatly when occupying the surface of the oceans is a viable alternative.
Consider this. Cities are effectively artificial islands. The UN estimates 68% of the world population will be urbanized by 2050, up from 55% today. In North America the number is 82% today. This works because to city-dwellers food production and distribution are already industrialized. It demonstrates the proclivity of humans to be drawn to concentrated urban centers when food supply is no longer an issue.
Also according to the UN, 8 of the top 10 largest cities of the world are located by the coast, and 40% of the world's population lives within 60 miles of the coast. Yet the coastlines account for only 10% of the Earth's land surface. Humans are drawn to living near the oceans. Why? It is a source of food sure, but importantly because the oceans are efficiently navigable it is a source of efficiently harvested food, as opposed to the energy it takes to farm the equivalent amount of edible biomass. For the same reason, trade with other population centers is more efficient over the oceans than it is over land. Every great modern city on the coast started as a sea port for trade.
Finally, consider the natural hazards of large population centers located on land. Earthquakes, cyclones and hurricanes, floods and tsunamis, wildfires, dust storms and winter storms constantly plague the inhabitants of land-borne cities and occasionally destroy them. Indeed, land of Earth is not a particularly hospitable place for large human civilizations. But as long as we have a dependency on it for food production we will be stuck there.
With completely industrialized food production it would be much smarter for civilization to migrate to living on the ocean surface on floating urban areas. Land-borne hazards would no longer be a threat. There are areas of the world's oceans where violent storms rarely occur, and without the threat of inland flooding just become wind events. Cities could easily occupy climate zones where energy use is optimized -- no extreme heating or cooling necessary. They could also be relocated over time as needed, perhaps on a seasonal basis. Trade between floating urban areas would be as efficient as possible occurring over water. Population growth would also be more easily accommodated. Habitats would not necessarily have to grow upwards from the surface towards the sky, they could grow downwards into the depths, ultimately helping to float and stabilize the entire constructs. Cities could effectively resemble giant artificial icebergs.
Were this to occur, the abandoned land would return to nature as another poster has commented. The pockets of land-based civilization left would be the crews of mineral extraction operations, the ideological holdouts, the vacationers and adventure-seekers, and the romantics.
It may also be how humanity might survive an extinction-level meteor strike.