As long as you don't install the takedown update @itsTwoUndead it'll usually let you finish the prize that you're working towards when the clock runs out.
So as long as you've started on the last prize you should still be able to complete it, bear in mind that any story line tasks from buildings or characters that you have unlocked will remain available even after you have updated, so just leave those and prioritise the event jobs.
Might be a safe idea to go into your settings and make sure that auto updates are turned off on your device first.
Best of luck to you, let us know if you make it. ?
P. S. Welcome to the forum and have a free "like" on me to help you towards your full member status.