If it happened overnight, probably a lot of people would starve. An individual not getting to eat at their favourite shit-house would just go to the shop and buy some “real food”. If everyone individual couldnt then suddenly the food shops are getting hit hard and would sell out in no time. Not to mention the panic-buying that would start up. People likely getting trampled to death and all sorts, stabbed up in the car park for their eggs and stuff.

If the fast food places quietly went away over a month or two everything would be fine.