The #WalkAway lot are leaving the Democratic Party because they believe that it is being taken over by Sanders supporters who are also controlled by whatever Russian or other forces they sincerely imagine to have given the world President Trump. And Brexit. And, oh, make your own list. After all, that is what they do.
They are hardcore Clinton liberals, and the Republican Party is welcome to them, even if they do represent rather a sad end to it. How many of them are there, anyway? Clinton lost to Obama in 2008, for all the good that he turned out to be, but even so. By any fair or reasonable measure, Clinton lost to Sanders in 2016. And Clinton lost to Trump, making her the only Democrat who could possibly have done so.
Both of her voters can #WalkAway, and the Democratic Party can win back the people who defected to Trump's relatively pro-worker and anti-war policies, daily frustrated by the Republican Establishment. Or it can be replaced by something that will.