What specifically are Sanders grievances with DWS?
Mostly just accusations that she's been rigging the process for Hillary, which I don't totally agree with even if she clearly prefers Hilly.
She's been a terrible chair for a multitude of other reasons though and I hope she gets replaced by Rybak or someone good next term.
This is how Bernie wins. The election is out of his grasp, but he still has important roles yet to play. It's good news for his supporters.
The most important thing is that the movement doesn't fizzle out with Bernie's candidacy. There's plenty of damage to be done downballot and in midterms.
Even if you're disappointed with Hillary as president because she isn't as liberal or principled as Bernie (I don't really have anything against her), the upside is that she's politically pragmatic more than anything. That means she could sign some really putrid shit if Republicans control Congress, but if liberals show up and put the Democrats in charge and stuff like free college, McCain-Feingold redux, $15 min wage, stronger Wall Street regulations etc. show up on her desk she'll sign them. The people who show up have a much bigger say than the ones who fold their arms and pout.
2018 will especially be crucial, as the first midterm of the past two Democratic presidents pretty much determined the course of their presidency. Clinton faced a full takeover by the GOP and pretty much capitulated to the right - the most he could do was water down legislation to not be as bad as it could have been (DOMA is awful but inherently preferable to going full constitutional amendment, welfare reform was much weaker than what Republicans proposed originally). Obama had a split Congress for four years and his legislative achievements came to a standstill. Had Democrats turned out in 1994 or 2010 we'd be looking at two very different political realities.