Thanks for the welcome dorkvader, and it's good to hear that someone thinks there is hope.
I've finished my "probing" as far as matching each switch to a diode and, as expected, the dead keys are all connected. Touching the far end of any of the diodes (well, the ones I've tried) to the controller chip results in a continuity beep while the dead column does not.
Hopefully the pic is of some use, the joints look dodgy because they needed scratching a little before my multimeter worked and the perspective's odd because it's a dull day and I kept getting flash shine - let me know if you'd like me to try and again to capture the whole board?
I don't think it's a cold joint on the keys as I didn't replace any in the dead zone - I replaced R and `with complete success, and G which I'm not 100% sure of as the pad has lifted. It is attached to space on the non diode side and it's diode on the other, so I'm hopeful, but if it needed to go through the board on the non diode side maybe not.
I was thinking to worry about G once the rest work as it's probably a separate issue, but maybe it's important?
Anyway, pic of the section in question:
Thanks again!