The first thing we need to do here is define our terms: what exactly is punk?
I believe one of the earliest references to it as a music genre is from the Ramones' "Sheena Is A Punk Rocker". The term came to represent a VERY diverse group of musicians and performance artists centered around NYC's CBGB rock club. It's important to realize just how diverse this scene was. You had Patti Smith's post-Morrison beatnik rock, Television's delicate, intricate intertwining guitars, Richard Hell's strange avant-jazz-funk (Hell is an often-unrecognized influence on Mike Watt, and a very interesting bass stylist in his own right), Blondie's "girl group" throwback, Suicide's avant-synth-pop, etc, etc, etc. As the movement grew, critics began to retroactively include earlier groups, sometimes from different cities, such as The Stooges, The MC5, and The Velvet Underground.
And so one definition of punk is "a bunch of musicians and bands that emerged from the late 60s to the late 70s that were basically unrelated musically but shared an 'outsider' aesthetic often driven by artistic intentions (or pretensions)."
As punk crossed the ocean, it became an intensely political thing, with groups like The Sex Pistols, Crass, and The Clash using it for a radical left or anarchist platform. So another definition of punk could be political in nature. Certainly by the 80s this phenomenon would cross back across the water and give rise to groups like The Dead Kennedys and MDC.
As the American punk scene surged into the 80s, it became faster, louder, and more abrasive, but (at least at first) retained a lot of its creative diversity. The aforementioned Dead Kennedys are a great example, as are The Minutemen, Mission Of Burma, X, Black Flag, Sonic Youth, The Zero Boys, The Descendants... I could go on and on. As a child of the 80s, this is probably my
definition of punk rock, but that's all while acknowledging that my definition is as subjective as any other.
By the late 80s, things were starting to get codified into the fast 8th-note power chord style of hard rock that many would consider to be the definition of "punk", and many others might consider its death. There were also a lot of bands that came out of the punk aesthetic that didn't fit into this new code, bands as diverse as The Cure, The Red Hot Chili Peppers, and REM, and a new word started to get thrown around: alternative rock. It was basically where punk started in the 70s: bands that were basically unrelated musically but shared an "outsider" aesthetic often driven by artistic intentions or pretensions.
By the 90s, groups that sounded pretty "punk" such as Green Day and Rancid (not to mention Nirvana) were getting regular airplay on stations dedicated to "alternative rock", and so at that point, I think what was left of punk basically became a part of the larger "alternative" scene.
So what the heck is punk? If you ask me, the most important technique for playing punk rock involves the middle finger. If you don't have that, it ain't punk.
Which is also why Frank Zappa is punk, and your pathetic emo band is not.
So, is punk dead? As a genre, probably. As an attitude? I hope not.