I know this is an old thread, but what's the update op?
I would have paid the debt, made your son get a job or something asap to reimburse you. I would have also told your son that if it happened again, he would face consequences for his actions.
He needs to face some sort of consequences now, than a brush off and a resuce from mom.
Police and drug dealers often have a mutual "understanding", alliance, work together, and on each other's payroll...they wouldn't have done much and perhaps turned a blind eye.
Unsure if they would have actually left you alone. It is a possibility that they would have harmed you, him, family friends, etc..tempted or forced him to take more drugs and more debt, made him work for them, etc...
I hope that you're out of the woods and they truly leave you alone....because it is possible that they can track you down.
If your son has a drug problem, moving anywhere won't solve the issue. Drugs are mostly everywhere.
If he has a drug problem, he will be doing these types of things repeatedly.
Hope all is well.
Perhaps he needs therapy and rehab