1) Only Ethereum is stolen
2) Even if users' coins are stolen, they might return all or most of them to their hands in order to keep their dignity.
how can they do this?
most exchange have an insurance to cover the lost when a disaster comes.I think Cryptopia will reimburse because its a security breach on there side. there website is not secured enough
Actually most exchanges don't have this insurance at all. If they did then the MtGox hack or the Bitfinex theft would of not resulted in a loss of funds.
Exchanges like Coinbase and Gemini have insurance but its for the fiat deposits. Usually nobody steals the fiat because its traceable. Usually when someone hacks someone's account, if they have fiat, they buy Crypto with it and then do a withdraw. And there is no insurance against that because once its confirmed on the blockchain its gone forever.
Either the theft is small to their reserves or they will issue a haircut for everyone like the Bitfinex hack a few years back when everyones balance was reduced by 33%.