Bettas tend to do fine without food for a few days in my experience. I go to conventions with my boyfriend every so often, and when we go, he has no one to feed his office Betta, and he does fine for a few days without food. But his tank is always cleaned before we leave, and he always has a normal meal right before we leave. He is is usually perfectly fine, but hungry when we get home, and has never had any hesitation eating again when we get back.
Keep in mind, though, every Betta is different. In general, though, your little guy should be fine for a few days without food :)