If easy fast food went away then the working poor would have to find time, money, and energy to source their own ingredients, keep them fresh, and cook them. Which is a tall order when you're already stretched to the breaking point working three shitty part-time jobs with ever-shifting hours. A lot of the people in that situation live in places with nothing but fast food in a reasonable distance, too.

Slower restaurants aren't an option - they take far more time and money then people in this situation have.

I don't know what percentage of those shitty part-time jobs are fast food, but all of those jobs are gone along with the places if we imagine snapping our fingers and decreeing No More Fast Food. Some might be substituted by increased demand at grocers?

I feel like one possible result is former fast food workers who do find some measure of fulfillment in the job of "feeding people" pooling their resources and creating some kind of neighborhood co-op kitchen that feeds their community, with a very different allocation of the money brought in by people paying for the food - more towards paying the workers and getting good ingedients than to increasing shareholder returns. Someone's probably gonna try to get rich off of doing this too of course. Depending on what kinds of resources they can acquire there might be a shift towards purchasing food from more local farmers, or even growing some crops themselves.

That's my first guesses, at least.