If Sanders destroys Biden then his supporters will have more incentive to go to Warren. And that would be that, unless Warren snatched defeat from the jaws of victory, or Bernie destroyed her.
The media will leap to Biden’s defense if “He’s not even a Democrat!” Bernie Sanders looks to be scoring punitive points against Biden, as they identify with him. If Sanders then had no choice but to go on the attack against Warren, oh my, I can guess how bad he’d get besmirched for that.
He’s got “blood on his hands for undermining Clinton”, would be the destroyer of good old Uncle Joe, and then he’d be the old guy trying to yet again stop a woman from being President.
Yes, Bernie can do better at scoring points, but he knows what his strategy has to be with “my good friend” Joe Biden, and then later with Warren. He’ll tell the truth and that will be like giving them hell.