Biden. No one else would get serious consideration.
Agree, it will be Biden. He’s dumb as mud but he comes across as a regular Joe, can play to the heartstrings over a lost son (not to war but to cancer), will have the full support of Obama and also the party, which would be secretly relieved to have Clinton, with all her current and pending baggage, gone as their nominee.
Ballots printed or some kind of deadline, early voting etc—may be too late to change?
Personally, I say Biden as that could continue the Obama agenda seamlessly, but maybe Warren to keep the female pressure on Trump. The leverage would be the ‘War on Women’ meme and bullying and sexism. You know the drill.