The PSU was out to get you :(
If it is still under warranty it should be able to be brought to the apple store to get it fixed but depending on how long it took you to turn the power off and (hopefully) turn a fire extinguisher to it the damage might be too much to repair.
If the board is damaged then it would probably be more worth it to actually just get a new one because I don't think it is covered under the warranty because of the fire damage.