Ultimately, the hand that feeds is the electorate. Robbing the nomination on superdelegates would spark a left wing Tea Party that primaries all the superdelegates that voted contrary to the wishes of their constituents.
This popular vote notion is misleading. The caucus states that Obama won and that Sanders has taken this year have no tally of popular votes. A state with a huge population like Washington state is totally disenfranchised by the use of a popular vote tally to justify anything.
Bill Clinton is committed to voting, on the convention floor, for whomever has the majority of pledged delegates, even if it’s not his own wife. I find it hard to envision a scenario in which he votes for Sanders but Hillary uses the superdelegates to overturn a pledged delegate majority. Don’t you?