I think that
1. We will always enjoy Rock, people still love classical composers who wrote hundreds of years ago.
2.Relatively speaking rock is not that old. Having said that I think that like in most things change is inevitable. Things evolve. It is amazing to look back at the genesis of rock and its evolution to this day.
3.Who knows what rock will become. Most things are cyclic. Meaning things go from good to bad and back to good again.
I hope you all don't think I'm a dork but I can't help being optimistic. Plus think about all the times in history when the pundits thought everything was going to hell in hand basket (the dark ages) and suprise things have a way of working them selves out (remember the Renaissance)