A wallet.aes.json downloaded from blockchain.info or emailed to on sign up contains everything needed to restore your bitcoins if blockchain.info is offline. The multibit desktop client is the easiest and quickest way to import blockchain.info wallet backups.
In the 'Wallets Wallets' side panel choose the wallet you want to import the private keys into.
Select the menu option 'Tools | Import private keys Import Private Keys'. The 'Import private keys Import Private Keys' screen appears.
Choose the private key file to import by clicking on the 'Import from. . .' button. A file chooser opens and you can select the wallet.aes.json file you want to import. Change the file type in the 'File format' drop down combobox.
If the import file is not password protected, the file is read and the number of keys and replay date for the file are shown. If the file is password protected, enter the password in the 'Password' field and press 'Unlock' to see the same information. If you have selected a double encrypted blockchain.info wallet backup a second password field will appear. Enter your second password and press 'Unlock' once more.
After the import, MultiBit then replays the blockchain from the replay date to find the transactions for the new private keys. For blockchain.info wallets the blockchain must be replayed from the first block. This can take up to an hour on a wifi connection (depending on the speed of the computer you connect to). It is best just to leave MultiBit to sync the blockchain on its own.
After the blockchain has synced and your balance is restored be send your coins to a new bitcoin address.