If Sanders isn't nominated and Trump is, the crossover or independent vote belongs to Trump and Republicans who aren't shy about saying they embrace the opportunity to work with him.
I'd assume the US Senate is already gone. So many of the turncoats are up for re-election. In OH, Senator Portman will be kamikazied for endorsing Kasich unless he jumps on the Trump Train.
Why do I care if the Repubs lose the majority in Congress? Nothing happened while they had a majority. So what?