Bernie voters, while yeah they love the "outsider" aspect of his candidacy, also support a long list of policies that Bernie has been fighting for over many years. I suspect that they will still support those policies, and realize that voting for Trump would only move the realization of any of those farther away.
Trump supporters seem to want the "outsider" aspect of let's go in and burn this baby down. I don't see as much common ground as many seem to see in this. Most of the people I hear saying Trump will get significant support from disillusioned Bernie supporters are Trump supporters engaging in wishful thinking. Hillary is far from being as liberal as the RW echo chamber likes to claim, but she's certainly not as far right as some of the Bernie supporters were trying to say either. Yeah, we hate to go back to "let's at least slow down the drift to the right" mode, but it's far better than the headlong rush to the right that the Repubs advocate. Bernie-ites may shy away from Clinton a bit, but I don't see a significant number of them switching that far to the dark side.
In a normal election, when the focus is on issues, Dems can win. If Trump and the media switch the emphasis to personality and celebrity we might get into trouble. Thankfully, Trump has shown no real character so far. You can see him trying to change that now, I guess, but how long can he stick to reading from a script he doesn't really believe in. He has celebrity, but how many people can he convince that he's that "guy you want to have a beer with?" The implication, in Bush's case, was that he would like to have that beer with you too, reciprocity. I don't see any of that in Trump.