During the event
You need to treat your card or wristband like cash. If you lose it, you will need to request a new one and topup again. Any remaining credits from your previous card or wristband will be lost as credits cannot be remotely revoked.
After the event
There are some cases where the UID can be recovered. This is especially possible if you topped up online. Simply log a request with email@example.com with the email address used to purchase your ticket or topup.