Hrm, well, yes, I guess that's SORT of true. Responsive firewall quizzes Asterisk for its registrations. If asterisk is restarted, those phones won't be registered, so they won't be visible.
However, the phones should automatically reregister, and reappear. Is that not what's happening?
If you're saying that EVERYTHING breaks, then that's wrong and terrible, and is a bug and you should be yelling at me about it 8)