I don't think Bernie will ever be able to win a drawn out 1vs1 primary. His best chance is for at least two of the Gillibrand, Kamala, Booker trio to exchange victories and survive for an extended period of time, while mitigating his losses in the South. He's never going to do good in the South or among black voters in a primary, but I do think he'll improve on his disastrous results simply because he's a known and well-liked quantity now. Opinion polls don't seem to show black voters actually disliking him or being more unfavorable toward him than the public at large.
But that was case in 2016. Black people didn't shun Bernie because he was unlikeable.
Black voters (especially older black voters) shunned Bernie because the demo is incredibly pragmatic and didn't buy his pie-in-the-sky bullshit, his barely concealed ignorance of issues specific to our communities and his scorn for the First Black President.
Bernie is a nice guy, but black voters know better than almost anyone that "nice" won't buy you a pot to piss in.