That doesn't mean they'd all vote Democrat though and he could still win in the electoral college if he lost the public vote. I think it's unlikely that he'll win, very unlikely, but not impossible.
It's scary enough that he's still likely to be the Republican candidate. If he gets the nomination, who knows what will happen. I feel like it's like Brexit in the sense that Trump voters and Brexit voters have a lot of passion about what they are voting for, while Biden voters and Remain voters simply don't.