Originally Posted by ChiefNWA

If everyone had already boarded before they realized this person was a no show in F, then technically it's up to the FA on board to move someone up, but certainly not a guarantee. There were still 15 upgrades on the list, so in the least, one of them should've been allowed to move up, especially on that lengthy of a flight.

If you're the last on the upgrade list and sit around the gate house until everyone is on board and there happens to be a no show in F, you'll get the seat. Otherwise, it's a toss up if the FA does anything about it.