I'm vegetarian, and I get lots of stupid questions about how I'll survive "the apocalypse" or whatever. Literally, I was asked that question about the apocalypse, specifically.
Anyway, after I addressed how I don't believe in xtian mythology or eschatology....
For one, how many omnivores have the ability to be full-time hunters, as is implied? I'd say it's close to zero, including the so-called "hunters" that do it for sport now. Oh, and what happens when you run out of bullets? The answer from some is "bow and arrow". Oh really? You know how to make new arrows? If you shoot arrows anywhere, you know how incredibly easy it is to lose them...not mention what happens when your neighbors all have the same idea - what happens when the whole place is completely devoid of any game?
It's not nearly as tacticool-sounding to talk about doing back-breaking work, working the soil, tending to your crops, saving seed, and so on. It sounds way more romantic to talk about yourself shooting animals and eating them, skipping the technical bits of how to clean and process said animal, including building a fire to cook it. Pulling a trigger is something any ape can do. I'm not so sure about the rest of it for any given person, most especially these big talkers. I'm not sure about my ability to start a fire from scratch, without a lighter/matches, especially under less than ideal conditions.
Secondly, how many people know how to properly clean and process things like deer? Oh and then there is storing the meat, without refrigeration... I'd would submit that surviving omnivores would have their diet drastically changed, too. Anything you kill you'd have to eat in short order. For people that know how to jerk meat, that might give it longer shelf life. I bet most people after such a collapse would get quite good at foraging for things like mushrooms and plants, as well as taking to learning something about raising crops. I have a feeling all of us would end dropping anywhere from a few to several pounds, again, assuming survival.
Lastly, it's not like being vegetarian is some kind of suicide pact, if the entire world is turned on its head, LOL. These people sit there and ask all these stupid hypothetical questions with a big smug grin on their face while the current situation is that we are more awash in options for fruits and vegetables than we've ever been in history and it's clear that they think because they are currently omnivores and have a gun or two and maybe a few dry goods in their basement that they have all contingencies worked out...