That is always the risk when flashing firmware, something goes wrong and the EPROM doesn't get overwritten correctly, then there is no firmware to even start or load the firmware to use the device, and in some cases NOT even able to get the device started and running to re-attempt loading a proper firmware. i.e. "bricking" it.
Other then sending it in, you can buy a new PCM and install it (or do it while you wait for Diablosport to return your PCM), or maybe find one at a Junkyard. Maybe the dealer can load the firmware with the wiTech tool, but its a good chance if the Diablosport couldn't do it, neither can the wiTech.