They absolutely won't switch candidates, there's no way in hell. That's even a higher softball then just letting Biden walk in. Biden could die and they would still weekend at bernie him to attempt the win against trump. It's too late, they made their choice and they aren't backing down now. They picked the wrong fucking horse again and it's their own fault.
I would have liked to have seen Tulsi gain momentum, I think she would have unified the center with the left better than Biden ever could. Bernie isolates the uber progressive so far left that half of them will vote independent before Biden... you would have had to have picked someone that Bernie supporters could get on board for, but again, you fucked yourselves and picked someone that centrists enjoy, but are starting to see how ill-prepared he is for going up against a guy like Trump. You need someone that is quick on their feet, not someone that's 20 brain cells away from having his applesauce spoon fed to him.