i would be looking for a 12ga for a survival gun way before a 22. slugs for the big stuff, #2-4 for the med stuff and 7's for the small guys (if food is needed)...just my 2 cents tho.
I think the .22 is for survival that involves collecting game to eat. A 12ga will protect you from any animal in the wild (maybe in Africa you'd need a G36 or a minigun, tho) but I just got a Dominion Arms Grizzly (12.5" bbl, Rem 870) and the damn thing weighs close to 10lbs so if you plan on taking that into the wild you should prolly bank on adding at least 10lbs to your pack with ammo. And a .22 shell takes up way less space and weighs less than a 12ga bird hunting round. That said, with a shotgun you can kill pretty much w/e you want.
I have no experience w/survival guns, but if you're packing light go with a .22 designed for the purpose. Although I bought that 12ga for bear defense, it's largely for peace of mind when I'm out alone rather than practicality... and if you're going into remote locations with big aggressive bears you're obviously taking a 12ga or high powered rifle anyways!