Unless the car owmer reports this as theft she/he will get nothing and lose the car. The insurance will want to know why there was a delay in reporting the theft and may well void the claim anyway.
The driver, sad to say, will probably get away scott free ! To PROVE he took it is going to be hard as no one saw him take it or crash it, also there will now be no way to prove he was drunk . As you can't prove he was driving there can be no charge of driving without a licence or insurance. Finger prints or dna are useless they can only prove he was in the car not that he drove it.
I can't see him admitting it as he is virtually certain to go back in jail having just got off 'tag'.