To guarantee the airline keeps your return, you’re required to check in and travel on the first legs and all the way to your final destination.
For example, if you booked London – New York – London, you can’t use the return as a single ticket from New York. You must fly London to New York first to be able to travel back on the ticket from New York to London.
The airline will automatically cancel all return flights if the passenger doesn’t take the outbound flight. Unfortunately there’s nothing that we as a travel agency can do about this. You won’t receive any refunds for the ticket either.