For some reason I can't fathom why anyone would want to carry a derringer, unless it is the only gun they own, and they can't afford another gun.
With the derringer you are limited to the number of shots, they are not accurate, as you said, they are hard to shoot (cock). There are many small guns out there that will make a much better concealed carry weapon, and definitely provide better accuracy, and more shots. Take a look at the Kel-Tec P-9 ($300.) or the Polish P-64 Markov ($150.), and there are many good small revolvers available too.
I think I would be looking to change guns before I got into a SHTF situation.