What the original posted posted is just fine. You bought a ticket from DL from A to B and back to A. You met all the rules. You did not buy a DL nested ticket, or a throw-away or anything else. If sometime between the outbound flight and the return you happen to go home, either by car, by train, bus or another airline, all is fine. This is not the government you know. DL can only dictate what you do on their planes and tickets.