If you choose sweep and the next day blockchain shuts down and is bankrupt(wiped off the face of the planet forever), are your bitcoins lost and unrecoverable because they got swept into the public key issued by blockchain?
They are swept into a new address or one of your old addresses in your blockchain wallet. If you have the private keys to all your addresses in blockchain wallet. You can import the private keys into another blockchain client, such as Multibit and Electrum, and transfer all the coins to another address.
Therefore, I can not stress enough to BACKUP all your private keys all the time.