You had better hope there is a huge pandemic that kills a huge chuck of humanity if this happens. Otherwise there will be many more predators willing to kill and take what they want than there will be farmers to produce the food. There would be no way to plant, tend and harvest crops and stock with all of the marauders out there. There will be chaos, IMO. The lazy will be the worst of the predators.
It's times like that where living way out in the boonies like I do would come in handy. Because we're almost 100 miles from anything that even remotely resembles a city, it would take a while for marauders to reach us...and by the time they did, the folks in my tiny little town would have already begun working together to store what we could and protect what we got. 90% of the folks that live here hunt and those who hunt normally have more than a dozen guns and enough ammo to use those guns for a year before they run low. Put all those folks together and my one little town could hold their own against an army
for a decent chunk of time.
Although, I'll be honest. In spite of what we see on the news every day, I try to think that people as a whole are generally good and most would be more willing to join a community and help than they would be to try to steal what others have. Sure, there would be a fair number of the latter, but I like to think that the former outnumber them by at least double. After the initial panic wore off, I think most people would be looking for a place to settle back down and build a new life rather than just pillage and rape for the rest of their lives.
And, hopefully there would be enough of the good folks that were armed to wipe out a good portion of the bad folks within a relatively short period of time. I know in the event that civilization ended, I
would be armed at all times and I would shoot first and ask questions later with any person acting shady.