Yes it's called change. When sending a transaction you need to "spend" all bitcoins from that address. Change get sent to a new address to preserve anonymity.
No the 1BTC would be spent. All the transactions are in a public database called the blockchain. Your wallet.dat only contains some bitcoin address with the corresponding private key. The private key let you sign a transaction and once it's been broadcast to the Bitcoin network then it's too late... The bitcoin has been spent.