As others have said, you can only try to comply with the law by sending to whatever address you have for them ("last known address") and it is up to them to arrange forwarding if they don't live there any more. Your state laws (or the lease) contain specific dates and means for compliance with the security deposit accounting.
The good news is that when or if they "sue you", you will have a way to contact them (their attorney), you will have defenses (you tried to send them the proper accounting) and counterclaims (for the entire cost of damages, not just the deposit). For instance, they broke the lease and owe rent until you found a replacement tenant; they damaged the place, they must pay for repairs; they forced you to sue them for damages, you might get your court costs and attorneys' fees reimbursed.
You can also file a criminal report for their vandalism (malicious damage) to your property, so that it is also "in the official record".
You can also send them an invoice for the damage, wait 30 days for payment, then send it "to collection", which screws up their credit, based upon their bad faith.