Bernie Sanders can use all the support he can get. He seems to be the only candidate with any sense so he needs the support from serious groups who can push him forward to where he needs to be. That being said there is no guarantee that it will help but you never know until you know.
Yes, the support of the HRC would help Bernie Sanders. The HRC is an organization with quite a bit of pull in Washington DC, and can be a powerful ally. However, he does not have their support right now, as the HRC has already announced that they are endorsing Hillary Clinton.
Let's face it, any publicity is good publicity. Mika telling the HRC campaign to not ignore Sanders will get more people talking about Sanders. Once people start talking, they start finding out more and more on a topic. People that did not originally know of Sanders' stands may look them up because of the press to see if they agree with his views.
Support of the HRC will not help Sanders' candidacy. Only an act of God will help his candidacy because first and foremost, Hillary is the anointed candidate and will not be stopped. Second, Sanders is a utter and complete crackpot whose views should be given as much credence as Pee Wee Herman's views on manhood.