of course you can still use your card if you have funds on it - having said that pre paid cards are going to be replaced by “pre paid” Current account cards in the new year - these new current account cards can be used in exactly the same way as the pre paid cards - when top ups by debit card are rolled out to all CA users 
- so shouldn’t be a problem to change before you go
shipping overseas is possible though I assume it would take a bit of time to receive as opposed to royal mail first class service