The primary will mostly benefit mainline Democratic voters.  The idea behind it isn't to give voice to independents or fringe elements so much as to drown out their Bernies with the votes of the rest of us.  
As far as the Senate race goes, Gardner will be beatable but he is a good politician capable of appearing moderate.  That's how he won in 2014.  Udall lost because he didn't run as himself, instead trying to be a generic Democrat with generic positions to appeal to Democrats (it worked for Bennet in 2010).  If Hick decides to run then he will win, but if it's anyone else they will have to develop name recognition and support so it become a crap shoot.