You're making dodgy assumptions here. This board is much like my binkenpds card; what you observe must only be taken as a point in time state of the signals without a direct correlation to what is actually wrong. In other words, you can't assume the CPU is dead or anything else is wrong based off this alone. It is useful to get a vague idea of if the system is running but that is all. Diagnostic tools like this are often mismarketed as a catch-all troubleshooting tool when they actually require a lot of skill and finesse to get actionable information out of.
A useful test is to hit the reset switch and see if the LEDs change at all. If /RESET is correctly working and the CPU is not entirely prevented from working by board damage, typically you'll see the lines change state at least once. Or if you pull the ROM, and the CPU is basically sane you'll see it walk the bus (count on the address lines).
That said, if you did actually manage to short 12v into 5v then you may as well chuck the board as everything on it will have fried including the irreplaceable apple ASICs
