At some point things don't happen in the absense of real advocacy, and advocacy that is determined by prinicple.
I don't doubt that HRC is e.g. a single payer person at heart, but she would never advocate for a "single payer option" i.e. that one of the carriers competing in the ACA marketplace is medicare for all. This is the path to single payer, let the governent compete. The government could offer a good plan at better prices and everybody knows it (as it requires no margin).
Bernie would advovcate for that, HRC would be looking at the 2020 election. It doesn't make her bad or untrustworthy per se or insincere, but her "practicality" makes her simply to slow an agent for change.
I know, I know, BO tried the whole change thing and was stone-walled. But, he was black. Not just that he was left of center, he was black and left of center.
While HRC would be better suited than Bernie to effect real change, she has already talked herself out of it (she did that back in the 1990s).
Her hybrid New Democrat stuff has just never really worked. Don't-ask-don't tell was counter productive. The various notions in banking deregulation and notions of increasing home ownership on the backs of it exploded. Repeatedly she follows solutions under the premise that one has to make a pact with the devil. The devil is winning.
So even if Bernie changes nothing and goes down in flames with regards to getting things passed, 4 years is a lot of time to own the bully pulpit and move the discussion left, far far left.
The good fortune of this cylcle is Trump. I think Bernie could beat Trump, so if Trump actually prevailed I think Bernie could articulate and win a class warfare candidacy, and follow through to use the bully pulpit effectively to move the whole window frame to the left.
That is what needs to happen. Solutions arn'te even in the the picture now, they are currently considered part of the edge of the frame.
The right would have to move torwards the middle and Bernie's successor could operate from what is internationally on the left.
Or not.