guys & gals

Im due to fly home on Friday morning out of Saudi Arabia and ill be flying the A380 back into Australia and i want to upgrade (economy flex ticket) to business class (to get a good sleep on the way home and of course enjoy the bar ). However there is a possibility (50/50) i may not make my flight if my reliever at my workplace doesn't show up on time. Now if this happens i will be re booked on another day, but if i have upgraded to business using my miles will i loose them if i don't make this flight or will emirates credit them back to me since i never traveled on that day???

obviously i don't want to upgraded using my miles and then not get them back if i don't make the flight. any help is greatly appreciated