Boki is almost certainly correct about the chip damage and you seem to accept that. Changing the flash chip is relatively straight forward provided you can do re-balling (it's a BGA package) however the hard part is to then re-program a new chip. If you can source a working chip from the exact same model with the same PCB then it'll work .... probably. Honestly it'd be much easier, and probably as cheap, to buy an entire working device secondhand.