They will send it straight back to you but an adult will have to be home to sign for the package.
I sent mine in for OBD also. I asked S&W what they did to the rifle and the only thing they would tell me was "Brought up to the latest spec". Which was frustrating IMO.
I have a DWC serial and the blue spring before the OBD. Good news is we are +600 rounds post repair with no issues.