I think we've decided Florida would be worse swing state, but I also see him doing poorly in Nevada. I don't think the Hispanic population would be as likely to vote for him as they did for Hillary, and with a far left candidate like Sanders most moderates in Nevada who voted for Hillary would likely swing to Trump or a third party candidate. I might be going a little far with this one, but I can see Delaware being a potentially competitive state. He lost the primary by a huge margin and Delaware tends to favor moderate Democrats, and would be really turned off by Sanders.
Delaware has a sizable black population and turnout amongst them would probably fall even more with Bernie instead of Hillary on the ticket. That's also why I have a hard time buying the argument that Bernie would've done a lot better in the Rust Belt. Does Bernie really make up enough votes in the white working class counties to offset turnout issues in places like Detroit, Philadelphia, and Milwaukee?
Bernie had a really tough time connecting to African-American voters because he kept connecting racial inequality to economic inequality, and I can't imagine him changing his rhetoric in a general election for black voters.