If they are paper tickets - a rarity nowadays but still in existence - they are much more than a piece of paper, they are a fungible asset.

Here's worst case:

If your ticket is lost or stolen, expect the airlines to:

1. charge you a $25 to $100 processing fee;
2. Require you to repurchase a ticket in order to continue your trip. If you no longer meet all of the restrictions on your discount fare (e.g., seven-day advance purchase) the new ticket may cost more than the old one did. In that event, however, it is generally the higher fare that is eventually refunded, as long as you don't change any of the cities, flights or dates on your trip.
3. Take from 30 days to one year and 30 days to process your refund request. This is due to a ticket being valid on most airlines for up to one year. If anyone uses or cashes in your ticket while the refund is pending, the airline may refuse to give you your money back.
4. require you to sign an indemnity if someone subsequently uses the ticket.


That's one of many reasons that e-tickets are much better. I'm hoping it was an e-ticket and all that was lost was the confirmation/boarding pass.