How would Biden win...

It's not surprise that Bernie would endorse Biden. He's been very clear that his battle was against Trump because Bernie believes in the system overall, (otherwise he wouldnt run for president) He still believes that fundamental change comes from who our leaders are and who is in government. However a lot of Bernie supporters don't. They believed in Bernie because he was outside the political establishment of corporate funded campaigns and corrupt politicians. He really believes Trump is a psychopath and Trump's character as certainly shown him to be a man-child and tyrant. That's why he pushes forward with the democratic part though flawed, because he sees American democracy at risk.
Now, in my opinion Joe doesnt stand a chance, he just doesnt have the enthusiasm that it takes for elections to be won like with Obama.
The only realistic way for Joe to win is publicly adopt Bernies platform. That is personally the only reason I would vote for him, and many Berners as well, because since the beginning we were about policies that improved the American public. So it will be up to Biden to win us over or not.
Meaning, once again the power is up to us. We are the ones that must demand from Biden to adopt these policies for our votes, because if we are democrats (as Bernie made us) then we are now Biden's constituents and therefore the people he is meant to appeal to.
I still really hate the DNC and I'm pretty sure they cheated as much as they could. But if the DNC adopts Bernie's platform, then I'd be a happier voter.