If users don't top up the credit for Digi prepaid after the validity has expired, will the balance of money be gone? Thanks.

Nope, the credit will be maintained and you can use it again provided you top up within the grace period.

Thanks. So the credit is maintained. What about the data ie. Free Internet? Can users use the phone to surf the internet or whatsapp by not topping up?

nope, data will be barred if you pass the credit expiry date without topping up..

you need to top up the credit

have long validity but no credit internet also barred.

i guess the number will end up terminated after some time when validity end