Steemit is an 'app' on the Steem blockchain. Steemit could disappear forever, and other apps and websites will still continue to use the Steem blockchain.

Just like bitcoin was created to showcases what it's blockchain was capable of because having a 'product' allows for non-experts to grasp, that is what steemit is to the steem blockchain. An example of what can be done on it.

If steemit disappears, you still retain all of your steem.....and if businesses like steemmonsters continue to use and grow, the price of steem will keep pushing up higher in price.