Originally Posted by
PV_Premier
they won't fly them empty unless there is some oddity with the agent at the gate and they don't process the waitlist.
^ This is correct. Regardless of what happens with U or F inventory, AS gate agents will always (as is required) process the remaining F seats if there are some empty. First to everyone on the upgrade list, and then to eligible non-revenue passengers.
Occasionally they may sell the upgrades at the gate, but that happens after MVP/elite upgrades and before non-revs clear. I haven't really seen it done recently, though.