I suspect that the DNC will be prepared for that by having backup credentials distributed to people in the galleries to quickly fill up the seats as fast as they are vacated so that viewing audience will never notice and the main stream media will be ordered to keep their cameras aimed at the speakers or they will lose their press credentials.
I prefer FR_addict’s thinking: the Bernie delegates should stay and start chanting “Lock her up!” That would be the best we could ever ask for!!