Your outgoing renters left three days early; you weren’t able to schedule a move-out inspection. The law says you have to return their security deposit, get the renters’ agreement in writing to keep some or all of it, or file for dispute resolution to claim against the deposit, but you don’t know where they are so you can’t do any of these.
You don’t have to do anything! It’s up to the renters to provide you with their forwarding address in writing. Once you receive it, then you have 15 days to take one of the above three steps. If you don’t receive their forwarding address within one year, the deposit is forfeited to you.
-- LandlordMentor