@maxdancona,
Extremely unlikely, but maybe more likely than Clinton putting control of the Senate by her party over her mission to win the White House.
It doesn't matter who is running, they all have extraordinarily oversized egos. At at this stage of the race, it's all about them, not America and not their party.
Primary races that split the party wide open don't usually end up very well for their ultimate candidate. Think Humphrey and Ford. Here though we have two divided parties.
If Trump gets the GOP nod, I imagine most of the Berners will hold their nose and vote for Clinton. Not all, but most.
However, if somehow Kasich pulls off a miracle or the party pulls someone like Ryan or Rubio from the sidelines, there a decent chance a bunch of Sanders supporters would vote for them over the hell-bitch they have come to the most as much as conservatives.
It will be interesting. If Clinton wants to unite her party, she needs to keep moving left, but if she wants to attract Anybody But Trumpers she will have to at least play up her hawkish tendencies...that which generates great distrust of her among the Berners.