On my last trip I left my ticket in a FP machine in AK and went back when I realised. Obviously it wasn't there but luckily it was my last day left on my old park hopper that I was using before I started my new ticket.
The cast member who was helping me told me that there wasn't a problem and that if I went to Guest Relations before leaving to hop to EPCOT that it would all be sorted out. He also gave me a FP card that could be used for the day.
Anyway I was pretty miserable for the rest of the day thinking that I would not be allowed to hop to EPCOT and that I had lost all my plus options that remained on the ticket.
On the way out I called into Guest Reataions to see if my ticket had been handed in (no - obviously), but the cast member asked if I had any other tickets and I explained about this being the last day before I begin my new ticket and she just swiped the other pass (my housemates) and just made me a copy within seconds! I was so surprised that she just took what I'd said to be the truth and just gave me a new ticket. She explained that the database checked my friends ticket (after I had told her they had both been used at the same dates and times) and found a corresponding ticket made a copy and gave it to me it after cancelling the old one.
This was a major lowlight of my holiday until it became one of the highlights a couple of hours later when I realised just how magical WDW can be and how helpful the CMs can be (particulary when you read all the negative posts here lately).
Anyway I guess the problem can be sorted out even easier if you take a copy or a digital pic of the tickets beforehand.
I just wished I'd seen the person who didn't hand my ticket in try to used it after it had been cancelled
I just can't imagine not handing a ticket in if I found one, especially thinking how it could ruin someones holiday if they had lost it.
Paul.