It is unbelievable that they are going to screw Sanders (and most importantly Sander supporters). They didn’t learn their lesson last time.
Sanders supporters will not show up and vote for Biden, just like they didn’t show up and vote for Hillary.
Berniebots would be more likely to have voted for HRC because of identity politics. There is no woke reason to vote for an old white man who isn't your idol.
My anecdotal evidence is meager, but the Berniebots I know have their eyes open more than they did in 2016, and they can see the fix being put in. The Stalinists among them want to see the convention burn, the Trotskyites are content with staying home on Election Day. Either outcome is good for Trump.