As they say they always get our password in encrypted form.is that really true?
that is correct. the wallet is stored on their servers as encrypted and opens up in your browser
is there service shuts down will i still have control over it?
since you can have the private keys and/or wallet exported, then yes you can have control by importing that into another wallet.
alternative:
use bitcoin core (it is full node meaning you have to download whole blockchain 7GB)
or use Electrum : SPV wallet meaning you only download block headers (30-40 MB)
blockchain.info is the not the most secure online wallet. I have heard few incidents when people wallets were compromised.
I think Coinbase is a better choice when it comes to online wallet.