Original ticket was entirely in C and LHR-ORD-OMA, with the ORD-OMA part operated by AA. It was rebooked by BA as LHR-EWR-OMA with the LHR-EWR in C operated by BA and EWR-OMA in Y operated by United. To claim anything with United, they had nothing to do with the ticket in the first place. On that day, he was not offered anything else except this one and he took it as the agent gave it.
Never offered any compensation.
The rerouted itinerary resulted in both: over 5 hours delays in destination and downgrade on domestic segment.