@scott93: The top part of the Discovery board is a ST-LINK/V2 debugger/programmer that can ALWAYS connect to the STM32F4 target device (on the back side of the board). This does not depend on the status of the firmware on that target MCU. You could not be a "bricking" type of situation with this board because you are not flashing the firmware of the STM32F4 using a erasable bootloader for example.
The USB bootloader that is built in to the STM32F4 device System Memory is based on USB DFU class. It cannot be erased or overwritten.