Steemit is a website owned by Steemit.inc. It's like Facebook or Google that has a company behind.
The STEEM blockchain however, is the open public decentralized blockchain that powers the content management system of all the Dapps (decentralized apps ) that is built on it.
Steemit and Steem is not the same thing. You need to understand that. Unfortunately it's been heavily conflated due in part to lack of marketing and user confusion and spread of false information by a majority of websites.
So if you're asking about the STEEM blockchain, technically as long as there is a node running the blockchain, it will survive. anyone can run a node with the right tool, and being voted as a top witness (node) pays VERY WELL.
So i dont see how people would give up running a node anytime soon.