Batteries left in this Gameboy leaked all over the PCB eating traces and destroying vias as it sat there for a long time. While it appears to be a lost cause, I think we can fix it!
The repair process started off by removing all the components near the bulk of the corrosion. This was done so that the soldermask can be removed using sandpaper. Once the mask was removed the damaged traces and vias became more visible thus easier to fix. The damaged traces were repaired using 30 gauge wire.
Once all the traces were repaired the focus was turned to the button contacts that were too far gone to use as normal. Custom replacement button PCBs from froggocustoms made this repair an absolute breeze! They were placed right over the bad contacts using holes to line them up then soldered into place using the ground tabs. From here wires are soldered to the pads on the PCB then to the Gameboy to restore the broken switch connection.