Bernie staying in the race benefits Hillary
We will get over a month to watch trumpy the nominee. Hillary will get a free month of the preview before she really has to dig in against him. She can release and anti-trumpy ad here and there, but can largely ignore him as long as the Dem primary is going on.
No other Dem will ignore him. He's facing a full frontal assault from the Dems. At the same time the goppers are dividing up and chooses sides. The party has been ripped in two. Every living republican president or presidential nominee has come out against him and are not attending the convention.
We'll get to see him get the different scrutiny that comes with being a nominee. Hillary isn't really spending much money or energy on the waning days of the Democratic Primary, compared to the past couple months. To the extent possible, she's resting and preparing to utterly destroy trump.
Bernie is providing cover. He's rounding up some more delegates to support his policies in the platform, he's bringing in new voters, too, but Hillary benefits from him playing this out.