> it really only lasted a single summer

"The Summer of Love" literally refers to one summer in 1967 not the whole of 60's counter-culture. Even Woodstock was in '69.

In terms of the various cultural strands then of course they lasted longer with many roots in 50's beatnick culture (bohemianism, poetry, LSD, Buddhism) to today where bands that played Monterey '67 and Woodstock are still touring and a "definitely not a hippy" in San Francisco might live in a polycule, micro-dose psychedelics while using a meditation app before writing a blog about effective altruism.