My question is what happened to my $625 paid? I know that it probably won't get refunded, but did it become part of the new ticket value / was it used to fund the ticket reissue? Or would a future flight credit be issued for it if the new ticket were lower value?
It would be frustrating if this were just evaporated as money wasted (both in terms of no benefit gotten for it, and also that the family member didn't check with me before making the change, etc.).
According to the T&C of the upgrade purchase, it’s forfeit upon any voluntary change. Some members have reported success getting it transferred to a new flight on the same route; I’m not sure how they’d deal with EWR-LHR vs LAX-LHR though. Keep your expectations low, remember that they owe you nothing, and call and ask what your options are.
It would not have been used in the calculation of the fare difference between the old and new tickets.