I deleted the game! If I reinstall it again, will the Leaf Tickets and other items I've purchased disappear?

If you link Animal Crossing: Pocket Camp to a Nintendo Account, it will be possible to continue using them after reinstallation.
 
Please see the answer to the Is it possible to continue using Animal Crossing: Pocket Camp as the same user if I change devices or obtain a new one? question in this FAQ for more information on the procedure for linking a Nintendo Account.