Most superdelegates owe their positions to what are now largely, and increasingly, pro-Sanders local parties. They are like Labour MPs.
Either President Sanders will be inaugurated in 2017, or a President from within the Sanders movement, perhaps never politically active before this year, will be inaugurated in 2021 in succession to President Trump.
Trump, at least one of whose own party's Senators has just unendorsed him. Yet who would still beat Clinton. But not Sanders.