Even though Bernie supporters may still be feeling the burn of him not being the democratic nominee his supporters can try and push his agenda by voting for Hillary. She obviously is much more likely to push those changes than Trump. One of the specific change Bernie advocates seemed to tout is his ideals on free post-secondary education. And while he was more in favor of that change than Hillary is, I think he would have a difficult time pushing this one through even if he were the elected to the white house. With our bi-partisan system, this is one ideal that probably would not make successfully make its way through congress. If Bernie Sanders truly want to see ideals becoming a reality they need to make sure they come out for elections where their legislative candidates are on the ballot as well.
Bernie Sanders and his supporters have a good hand to play at the Democratic National Convention. The Sanders campaign has earned enough delegates that it can demand to write much of the Democratic Party's platform for the presidential election this year. Also, Sanders can demand that he be allowed to give a speech on the floor of the convention. In short, yes, Bernie Sanders and his supporters can still get the changes they are demanding.
Bernie Sanders and his supporters will not get the changes they are demanding because those ideas for change are so far removed from reality and so radical that no one in their right mind would vote for them, let alone even consider them. The best thing that could have happened is his losing the nomination. He is a crackpot.
Bernie Sanders and his supporters are not likely to get many of the changes they are seeking. Hillary Clinton has a commanding lead among delegates, and he has lost a lot leverage. After losing California by a wide margin, his negotiating power diminished. He will continue to fight, but Clinton has no reason to negotiate.