Yes, I think that rock music has clearly been on the decline.
'Rock' as the (counter)cultural force that started with the Beatles and Stones was, IMO, ended somewhere around in the mid-late 1990s, ignominiously, with the advent of rap-metal. There was a period of time when certain rock styles were re-hashed and/or mashed together, throughout the early and mid 2000s, but despite some of these bands garnering audiences and good reviews, the sales and the venues they played told the story of declining public interest. It's no coincidence, IMO, that it was at this time when it became kosher for virtually anybody who ever sold anything between the 60s and the '80s to be rebirthed purely as nostalgia attractions during this time. As the years passed and hardly anybody new of the "rock" milieu taking the place of the older bands, the general demise of the genre seems pretty apparent to me.