Even if they dropped Biden or he dropped out, it would not go to Bernie as Biden's delegates would likely unify behind someone else. Bernie was rejected by the majority at this point. You'd get some messy convention and who even knows who would end up on the ticket.
It could, but it would require party heads to put their foot down and go on Biden hard, since I doubt Biden would willingly step down of his own accord. Which I don't see the party doing, whether for optics or for attacking a highly regarded member of their party.
Better that we kick a stink about it now before it really is too late though.
This is depressing.