Yes you're correct - it's a lost cause, that consistent time of 8 sec until reboot is a sure sign of flash failure. It's holding preboot because that puts far less demand on it than a full boot.

White it's technically possible to replace the chip, very few technicians have either the knowledge or the equipment to replace and reprogram it and it's definitely not economically sensible anyway.

Any still working parts are saleable if you can be bothered to strip it but i'd just buy another identical unit and keep that one for spare parts.