Opposite to what? When you deposit into an exchange you are not given fiat value into your exchange balance, but you are given only RIGHTS to trade onto their exchange with their offered value of your deposited asset.
You have to consider that, like crypto hot wallets, an exchange also have "fiat hot wallets" to address user fiat conversion requests on daily basis.
This means that part of the crypto coins must have been converted in to FIAT before the takedown. To allow users to withdraw if requested.
Exchanges usually convert a percentage of users' coins daily to feed FIAT hot and cold wallets.
Therefore, since the "FIAT hot and cold wallet" are presumably lost, a complete refund of all the assets is quite difficult, especially on the FIAT side.
But hey, I hope I'm wrong
You can't convert crypto into fiat. You can trade one for the other with someone but you cant convert them, it's not alchemy, it's just a change of ownership. Exchanges like BTC-e have bank accounts which people transfer by wire and other means funds into to purchase BTC-e "casino tokens" called USD/RUR/EUR which they can gamble and trade with other BTC-e users for fiat or crypto tokens, coins are not changing hands, only an IOU is changing hands in the BTC-e database. The bank account balance doesn't change for those trades, it only changes when people cash out their IOU or make a new deposit, or when BTC-e take their fees out, so the balance should be high unless seized. Same goes for their crypto wallets.