Re: 7.8 BTC lost due to an error in blockchain.info

Do you have your .aes.json file/s? If not, could you check your email account?

Maybe importing on multibit Classic v0.5.17 or below could work *https://multibit.org/release-info/classic/v0.5.17.html

If he has wallet.aes.json then he could try decrypting it with blockchain tool? (https://github.com/blockchain/my-wallet-backup-decryption-tool)

if you don't have the backup or unable to find it, try this thing below.
https://blockchain.info/wallet/ {Your ID } ?format=json

then try to decrypt it with blockchain tool.