Not an elder statesmen, but had a sibling with a similar (not drugs just estranged) propensity to return to the nest when things were dire monetarily. They stopped offering money but offered council and the relationship has slowly gotten better. She needed to see them as something other than a bank for that to happen.
Other than offer to pay for a lawyer, which the state will provide, what else can you do for your son besides sitting in the courtroom? Are they looking for you to pull out a cape and save the day?
From what you said, you have tried. At some point he has to deal with the decisions he has made. Using drugs was his decision. Leaving your home was his decision. Quitting college was his decision. Court/jail will be HIS consequences.