i have a quick question.

I am planning to do a LAX-HKG roundtrip upgrade
what if one get both ways confirmed, but the return trip turnout (an open ticket) rescheduled and the U inventory is not available on the new date, what will the agents do?

p.s. Actually both inbound and outbound (in August!) U inventory happened to be sold out in my case. If I manage to do an instant upgrade for inbound, and then instant upgrade on outbound travel, how will mileage be deducted? 40000x2 or 70000?