Depends a lot on why the family chose to leave and what they said. Moving out of town? Feel free to come to banquet. Outgrown/outleveled a compulsory gym? Feel free to come to banquet. Feel the other gym is better coached or has a less toxic environment? You can see why the coaches and owners might not feel like celebrating you after you called them inferior or toxic. You still have an anniversary dinner with your girl/boyfriend after your breakup? Nope.
Now, the idea that parents and kids won't communicate if people don't come to banquet, that's just silly. Of course they will.
Now, the idea that parents and kids won't communicate if people don't come to banquet, that's just silly. Of course they will.