The only problem I'd have with it is the leavening going weak. Baking powder tends not to age well, so I stayed away from self-rising solutions when I camped. My advice would be to fix it per instructions and if I didn't get enough bubbles in the batter, I'd hit it with a teaspoon of baking powder.
I've made pancakes from much older mixes without a problem. After a couple of years, the flour starts to get stale. It's still edible, but not very tasty.
