This very much depends. Are there technical ways to restore this? Something like a jumper to make the flash storage writable. This would be possible with access to the firmware source code. So yeah, they can fix it themselves. Who is responsible? If the device is bricked after this: the company.

Build locked up products? Die.
Build in fuses? Better make those chips accessible by providing the plans to build them, otherwise refund your customers and die. Now everyone can build them, this won’t be a monopoly and everyone wins.