I was giving consideration to a 9mm carbine as an "end of the world" type gun and it got me wondering how far out it would be effective? You could try adjusting the powder type to optimize the burn rate for 16" (I'd assume more 9mm is made with 4" barrels in mind), and also choose a more optimal bullet weight. Do you think it would be reasonably effective at 100 yrds? If not 9mm, what about .40, .45 ACP, or something else (maybe .357 sig or 10mm)?
My thoughts are that if you could reach out that far effectively with a 9mm carbine that would negate most of the capability lost by not having something like a .223 rifle. This is assuming you were working in a suburbia type area where you generally don't have very long uninterrupted areas of terrain. Then of course you can use the same ammo in your handgun as well, and its cheaper than .223.