Originally Posted by
findark
I would clarify this - whatever OP wants to do, he needs to tell UA about it in ORD. Just no-showing ORD-LAX and buying a new ticket is a bad idea.. go to the counter in ORD and ask to get ORD-LAX canceled and whichever of refunded, ORCed, or rerouted to DTW (depends on how nice UA is feeling) first.
This is good advice. At a minimum I'd call UA to cancel, though I wouldn't worry too much about the consequences of simply no-showing (provided he doesn't make a dupe booking on UA).