They say this about every genre of music once in a while, and it tend to only be true for the REALLY popular genre's e.g. Disco, early British Punk, Grunge (not exactly dead, just not as popular), Techno (still going I guess... but still kinda sucks.) Rock will keep going with every single generation, sure it may take a detour everyonce in a while and wander into sucksville e.g. Indy Alternative rock.* Rock will be around as long as there are guitars, punk and metal will loiter forever as long as there are ticked off Teenagers around the world, and poprock will die out when the Jonas Brothers finally decide to stop making music.
*I acknowledge that some Indy/Alternative rock can be good, but the majority of the music from this category that I've heard is really sucky.
And why has no-one mentioned MASTODON?!