20-Year Prospect
Will pizza still be around in twenty years? Boy, we hope so, and if you hear anything different, promise to tell us first, okay? We'll need to sign up for that Mars One thing.
If pizza is around, then pizza parlors will be around, and will subsequently need someone to operate them. Provided you can actually keep yours open that long, there's no reason to think that the industry won't be kicking long after you aren't.
Sure, health fads will come and go, and restaurant real estate will be increasingly sparse, but pizza is, like, a universal constant. So don't worry about the occupation at large; you're your own boss, so save any worries you may have for your own personal stake in it.