They will have a hard time doing anything on the Steem blockchain. If the accounts that lose the SteemitInc delegation don't own a at least a couple STEEM they won't be able to post/comment or upvote much. Maybe not even at all if they have literally 0 STEEM. Then they can't interact with the STEEM blockchain.
STEEM is Bandwidth for the Steem blockchain. It's like the internet is for your browser. Without it, you couldn't load any pages. Its as simple as that.
Users that didn't have the needed amount of their own SP and have lost the SteemitInc delegate, would have a really tough time trying to interact with the STEEM blockcain. Like you would, trying to open a youtube video with 0.0007 Mbps download.