The answer splits into two trajectories. The simplest trajectory is where those individuals changed their values as they aged into what are traditionally conservative values – favoring lower taxes, preferring stability to dynamic change, etc. This treats “conservative” and “liberal” as constants, and remarks the change in individual behaviors.
The second and more interesting trajectory looks at how the definition of “liberal” has evolved. A second contingent of those old 1960s hippies has stuck to their hippie values, but has seen the definition of “liberal” separate from, and then become antagonistic to, those values. The new “liberalism,” to them, seems restrictive, segregationist, and puritanical – in a word, the antithesis of a 1960s liberalism that was restriction-busting, radically integrationist, and non-puritanical. This branch of 1960s liberals indeed no longer fit the category “liberal,” but nor have they altered their values in the direction of conservatism. Unlike those in the first branch, these 1960s liberals have simply become outsiders, equidistant from today’s conservatives and today’s liberals. They see today’s liberals and conservatives both as essentially reactionary formations, restrictors of freedom, each trying to enforce its own norms against all dissent, with no one left to represent the more radical liberation of the 1960s vision.