Folders are unnecessary if you're willing to carry a fixed blade.
Don't get me wrong. I've got a ton of folders including Spydercos and ZTs. They're sexy as hell and they excel at convenience and covertness. But I wouldn't count on any of them in a survival situation. A folder is, by definition, a knife that's broken by design. If the SHTF, I'd go for my Swamp Rat Ratmandu and my Swisstool Spirit before I'd pick up any of them.
If you're going to get a folder, my recommendation would be to reframe your thinking. I'd suggest you get one that meets the following criteria:
Slices well
Holds an edge
Sharpens easily
Carries comfortably
Then leave the hard work for your fixed-blade.