Any hope that the Democrats had of winning went out the window when Yancy and company deliberately split the party. I agree with you on the vote counts as they ended up and how combining the opposition vote counts really only changes two small states with seven EC votes.This is inaccurate. Take a look at the Results by state section of the Wikipedia article on the election. Lincoln took over 50% of the popular vote in every state in which he won the EC vote except CA & OR (7 EC votes). That means you can combine ALL the non-Lincoln votes into one and he still wins 180-7=173 electoral votes, 152 being required to win. Lincoln won the election because a decade of excessive demands and actions of slavery proponents pushed a majority of Northern voters into the Republican camp (heck, those actions created the Republican party). Yancy & Co. didn't have to divide the Democratic party to throw the election to Lincoln and realize their secessionist dreams. But of course, they weren't going to leave it to chance.
EC I don't think this is accurate. If you look at the EC, I think you can combine the votes of all other candidates, including fusion tickets, into one, and Lincoln would only lose 7 votes (CA & OR).
However, I do think the Democrats had a shot if they had united and reconciled at the Charleston Convention. If Douglas had a united Party behind him, he would have campaigned differently. The states that were closest were Illinois (11 EC votes, Lincoln 50.7%) and Indiana (13 EC, Lincoln 51.1%). Douglas would have to flip both of those if he wanted to win, but he had beaten Lincoln in the 1858 Senate election in Illinois while Indiana went for the Democrats and Buchanan in 1856. It would not be hard to imagine that change.
Any chance at that probably went down the tubes with the disaster of the Yancy walkout in the Charleston Convention.