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 Can I still use my Animal Crossing: Pocket Camp save data if I get a new device? question in this FAQ for more information on the procedure for linking a Nintendo Account.