Steemit-based media Cryptocurrency it is on something called blockchain, blockchain characteristics make unlikely companions steemit postings will be deleted, because there is the eternal character of Blockchain characteristics.
All postings on the steemit is stored in the database Blockchain perfect and eternal nature or cannot be changed. This system stores all user databases include postings, upvote, amount of reward for author and curation copied in Blockchain.
But can replace the posts with the remove and replace with other writings and replace also the tags.