This really depends on what platform you are using to browse the Steem platform.
Steemit.com for example displays posts/comments with negative payouts like the one below. In which one has to click first the "Reveal Comment" button to show the comment that user did along with all the replies to that comment. Other platforms like Busy.org or Partiko however, just let it be. This is because Steemit.com collapses the parent post/comment that got a negative payout.
Here in Musing though, answers/questions with negative payouts are not hidden. Musers can still see your question as backed by this very question of yours which got downvoted,
Depends on voter's voting weight and steem power.
For example, a person with 10 sp flags your comment, it won't be hidden. But, if person with 10k sp flags your post with 100% voting weight, it will be hidden.