I found a ticket in a fastpass machine, and I was horrified! It was a 5-day hopper plus ticket, it cost well over $200. I asked the CM that I turned it into, what would happen if an honest person like me didn't turn it in? Are the owners out a pass? They told me NO...they just have to go to the ticket booth and would be issued a new pass.
Now, I am not sure you would even need your reciept. Some people who order over the phone don't even get a reciept. When I picked up my passes, she had ALL of my purchases of passes from the past two years in front of her on the computer. So, I am sure if someone lost their pass, they could go to the ticket booth and it would show that they did in fact purchase a pass, the CM could cancel the lost pass and issue another. They can even check by way of the ticket number how many days were left on the pass.
Basically, Disney has you covered if you ever lose your VERY EXPENSIVE pass. But I would still be very careful and make sure you DON"T lose them. I think it is terific of Disney. Alot of other places would not care if you lost your ticket. Not their problem, right?