Cities are grown on trade. Take the trade away and they die quickly. The dominant theme to start with, once immediate survival is secured, is emigration. There will be a lot of people who become unemployed virtually overnight. Unless someone manages to soak up all this excess labour, they will need to leave, even if the food is free (free food could put landowners out of business, btw., unless they manage to adapt to the situation). People still need clothes and housing, and they will want hope that things will improve for them. The city will enter a rapid downwards spiral as reductions of the economy means loss of population, which again leads to economic drops, etc. This will continue until the city recovers its economical equilibrium.