Bernie's numbers were huge and dominating with people under 40. It will take a decade or two, but, i think Gen Z and Millenials will finally usher in more progressive change in the Democratic party.
I share your hope. That being said, my cynicism says that a decade or two might be too late, and that the Democratic party might try to exploit the ratchet effect to neuter any left wing candidate, as is the interest of their donors.