In a total collapse, given the demographics of our society (elderly, obese, medically dependent, etc.), I think a 33% survival rate would be a high number. More like 1 in 4 will make it when you factor in human nature, external involvement, and weather. And those will be a tough 25%, with a larger than usually bunch of flat bad folks in the mix. Probably 1 in 5 today are disposed for the kind of agrarian communalism folks have mentioned here, and most of those unskilled for the tasks. Which means a lot of crop loss in the first season due to human error, which translates to probably another 10-20% casualty rate. In 2-3 years post a major event, without any external issues, I'd say 75 million, most of whom have banded together and established some rule of law, plus another 5 million who choose to live outside and prey on the others.
My original thought about sustainable hunting was with that context in mind. I've concluded based on this thread and others that I will not be relying on firearms and ammunition as my means of hunting. Even in a community, lacking the ability to make BP, primers, etc., I would not want to expend irreplaceable ammo on chores I can accomplish by other means, like bow & arrow, sling, rabbit stick, traps/snares. I am told I think too much and have too much imagination ... perhaps. Or perhaps I'd just hate to be cursing myself a fool then for not thinking hard now.