The way I understand it, if one Democrat hasn't reached the clear majority, it goes to super-delegates.
"In a contested convention where no majority of minimum 1,886 pledged delegate votes is found for a single candidate in the first ballot, all superdelegates will then regain their right to vote on any subsequent ballot necessary in order for a presidential candidate to be nominated (raising the majority needed for such to 2,267 votes)."
This might happen .