Block 0 of most SSDs is typically used for storing a whole heap of data that's pertinent to the operation of the SSD, most typically the image of the firmware.

Block 0 of most SSDs is typically used for storing a whole heap of data that's pertinent to the operation of the SSD, most typically the image of the firmware. If you scramble that the drive's controller won't be able to boot. It then becomes a chicken and egg problem because if the drive controller can't boot you can't flash new firmware into the first block. You can possibly throw the drive back into debug mode and reprogram it like they do at the factory but that involves a lot of expertise and screwing around with low level hardware. From the perspective of an ordinary user the drive is pretty much bricked. In Apple's case there's a BootROM literally laid out in the mask of the secure enclave. It's read-only and it's permanent. This BootROM has a fallback that can be used to at least load a new iBoot image from scratch. So even if the NAND on the flash is scrambled you can still boot the machine in DFU mode, install a new iBoot, and bootstrap the machine from there. You won't have the data but at least your NAND still works.