Good afternoon,
***ouch, that's bad.*** I am gonna say that this thing is kinda screwed. First step is ***always*** to keep the laptop off and clean the corrosion.
Now, i could bore you all arvo on the reasons why this thing could be screwed, but that's not gonna fix it. So hopefully this will:
# Disconnect the battery by removing the connector
# Remove the board
# Take some Alcohol and clean all the green shmoo (corrosion)
# Visually inspect the board and ensure nothing has blown
# (If nothing is burnt/broken) put it back in the laptop and try powering it up. If it smokes then your done for. If it powers up and display an apple logo, that's good.
# (If something has burned) If you can find the audio board then you can fit it into the machine or, it's the end of the road without assistance from a professional tech
Hope that helps :)