I think you have Warren and Sanders flipped. Sanders only became a Democrat recently and with the best will in the world, Sander's doesn't score particularly well on "Plays Nice With Others". The institutional Democratic Party doesn't particularly like Sanders and the amount of sniping and nitpicking on his candidacy from grumpy Third Way Democrats will sink Sander's presidential campaign and make him an American Corbyn.
Warren, on the other hand, is broadly similar to Sanders in what she can get done with an obstructionist congress (ie: who she will appoint to cabinet, judges, and the alphabet agencies) and the institutional Democratic Party likes her more as she is a better 'Team Player'.
Sanders would be far better on the outside, working to keep popular excitement high. One of Obama's biggest election mistakes was to allow the popular excitement to dissipate. He had assembled a strong and excited coalition, that was more or less allowed to wither/not used for state election; and the Democrats paid a heavy price for that.