Much like what is happening now in the Republican party.
There are some things you can objectively say about that. A populist tyrant? We all agree that Hitler is almost the definition of tyrant. yeah? Alright, let's actually compare the rise of this tyrant with what is happening in the Republican Party.*
There are some people who compare the rise of Trump with the rise of Hitler and say 'Hitler was democratically chosen'. This is only half true.
While it is true that Hitler was popular among some people, he wasn't necessarily among the rest. The Weimar Republic was divided and there were also people who wanted to overthrow the government in favour of a communist regime.
However, fascist regimes not for nothing rely on violence and intimidation as a part of their philosophy. So, in 1932 The Brownshirts took to the streets and basically bullied or downright forced people into voting for the Nazi's. And so Hitler was 'elected'.
And there ends the comparison of Trump with Hitler. Hitler was 'elected'. In such a system, superdelegates can play a major role as a veto by the elite.
As much as I despise the man, I don't think Trump's supporters will organize as much as the Brownshirts did en bully people into voting for him (on the same scale, there may well be some individuals that do, I wouldn't put it past them).
If Trump is elected, he is elected, sad as that may be. Using the superdelegate tool against him would mean the end of the Republican Party, and they know it. It would be a big middle finger from the elite to the American people.
In Hitler's day, if superdelegates existed, it would mean nothing at all. The chancellor already ruled by emergency decree, and the elite was actually partly favouring Hitler over the existing Weimar structure. The elite was already using its authoritah in undemocratic ways.
Tl;dr: if Trump was a tyrant like Hitler, superdelegates could be super useful. But Trump isn't Hitler and this isn't 1932. He's a populist, he's a demagogue, he's a warmonger. But he's not a tyrant.
So yeah, it's a failsafe. But not one they will actually use unless it's absolutely clear that it's needed.