There aren't that many people working on farms in developed countries. In the US, only around 3 million people (or <1% of the total population) work on a farm. [0]

In other countries where many people are involved in agriculture, the pending industrialisation/automation of farming will probably have a similar impact to what happened in North America and Europe over the 20th century: more people will move to urban areas and add value to the economy in other ways.

[0] https://www.agcensus.usda.gov/Publications/2012/Online_Resou...

The answer is "whatever they want". The big problem facing governments everywhere right now is how to jump over the little gully of poverty that comes right after the change to get there.