If they actually do that, Trump will get a lot of cross over votes from the discarded, but very competitive Sanders voters. Not because they want Trump, but they'll be teaching THEIR 'Pee a lesson too.
From your lips to God’s ears.....but I think that they will try to assuage the Sander’s supporters with Warren and will make Bernie a very public offer that he can’t refuse...such as Education secretary pick, or some such thing. Then Bernie will sign off and everyone will be happy.
That being said, I really hope you are right.