The issue is that most Saudis don’t work. Most of the work done in that country is done by “lower classes” of non Saudis. So when the tap dries up and they all have to work. What do they do?
Realistically - they'll get deported to their home countries. There's no government on earth that will tolerate a non-citizen, non-refugee as a public charge with no prospect of being productive in the future. Foreigners are politically convenient scape-goats for all that is wrong with {ECONOMY|JOBS|CRIME|SERVICE DELIVERY}, and politicians will politic.
The migrants will try to migrate somewhere else that has work.