Just by looking at that picture, the main damage is obvious - it also looks like it took out a few nearby components.
I don't have a schematic - I don't know of any out there for these.... if anyone here does, I'm sure they'll point you in the right direction.
Personally, I think your mac is dead. It has some value left there in at least the screen.
If you could find out what the components are, and could change them.... it MAY work.... but, like you say, you're not really sure what even caused the original problem. Was something split on it? if you replaced those with obvious damage, and powered it on, would you just burn them out again?
Giving the board a proper inspection may reveal more clues, but on the face of what you have here, as a repair shop, I would not want to waste my time. The only feasible repair at this point, would be a full motherboard replacement..... but you would have to weigh up the cost of that, vs selling your damaged unit, and buying a working second hand, or splash the cash and get a new one (slightly discounted by selling the faulty one)