Co-signed on an Auto loan and it went into defalt.?

I am a proud co-signer of a s bag who left me with a defaulted auto loan and has Absolutely no intention of paying it back. I have been threatened by so many debt collectors to pay this loan. I offered to make payments but they want all the money NOW or nothing at all. Or they will accept $500+ payments every month. I don't even think that's what he was paying for the car. What I want to know is what is the worst care scenario and most probable scenario if I'm eventually taken to court over this stupid mistake I made?