Any exceptions to only using the return half of a ticket?
 

I had a flight booked on UA that was connecting up with a flight on AC (booked on separate itineraries and separate airlines). AC flight was canceled, so I had no other options than going out a day earlier on AC (consolidator ticket), making my UA arriving a day late for the connection. Are there any exceptions for missing the front end of a ticket, but still using the return? All other options are out because ticket was booked on a voucher, making the cost of the change, the same as buying a new ticket. Help?!?

If you don't take the outbound flight, the rest of your ticket will be cancelled.