Recent polls show Sanders farther ahead of Trump than Clinton is, and he'd get a higher percent of her votes than she'd get of his if the other drops out, but the Clinton name in itself guarantees a larger Republican turnout. I'd bet she can beat Trump but there's still the threat of the email investigation. Trump and the Repubs look pretty despicable right now ... but who knows? So I'd be really worried if Bernie surrendered now.
My hope is that, aside from some feel-good wording in the Dem platform, she takes on Elizabeth Warren as VP. I heard her speak on a couple occasions recently and she's really found her voice. She has a very assertive message now, all in with Bernie on the important issues, and I would expect HRC would not be able to keep her hushed up. Even if they let her go after the first term she would gain the footing and the following for a future campaign. Otherwise the causes that Bernie stood for will fade way as we are all assimilated back into our silos.
I've been aware for some time that BS polls better against Trump. Irrelevant at this point. Equally so wrt to Warren. I like her, but it would be too radical, and Mass will go for HRC without her. Besides, she's more effective in the Senate. Maybe Treasury?
Sherrod Brown is an interesting choice.
But you didn't address what Bernie should do.